…g_configuration

Fixes: hashicorp#1657

Before this patch:

```
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: panic: runtime error: index out of range
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4:
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: goroutine 2687 [running]:
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: github.com/terraform-providers/terraform-provider-aws/aws.extractProcessingConfiguration(0xc420c8f650, 0xc42080b710)
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4:   /opt/teamcity-agent/work/222ea50a1b4f75f4/src/github.com/terraform-providers/terraform-provider-aws/aws/resource_aws_kinesis_firehose_delivery_stream.go:541 +0x2ad
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: github.com/terraform-providers/terraform-provider-aws/aws.createExtendedS3Config(0xc4203ecc40, 0xb)
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4:   /opt/teamcity-agent/work/222ea50a1b4f75f4/src/github.com/terraform-providers/terraform-provider-aws/aws/resource_aws_kinesis_firehose_delivery_stream.go:483 +0x479
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: github.com/terraform-providers/terraform-provider-aws/aws.resourceAwsKinesisFirehoseDeliveryStreamCreate(0xc4203ecc40, 0x29c5ec0, 0xc421689a00, 0x24, 0x40555c0)
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4:   /opt/teamcity-agent/work/222ea50a1b4f75f4/src/github.com/terraform-providers/terraform-provider-aws/aws/resource_aws_kinesis_firehose_delivery_stream.go:808 +0xbc5
2017-09-12T11:56:41.138-0600 [DEBUG] plugin.terraform-provider-aws_v0.1.4_x4: github.com/terraform-providers/terraform-provider-aws/vendor/github.com/hashicorp/terraform/helper/schema.(*Resource).Apply(0xc421937ec0, 0xc420c4a820, 0xc420816140, 0x29c5ec0, 0xc421689a00, 0x1
, 0x28, 0xc420c8edb0)
```

After this patch:

```
terraform-testing % terraform apply
aws_s3_bucket.bucket: Refreshing state... (ID: tf-test-bucket-72)
aws_iam_role.firehose: Refreshing state... (ID: tf_acctest_firehose_delivery_role_72)
aws_kinesis_firehose_delivery_stream.broken_tracking_autocomplete_stream: Creating...
  arn:                                                      "" => "<computed>"
  destination:                                              "" => "extended_s3"
  destination_id:                                           "" => "<computed>"
  extended_s3_configuration.#:                              "" => "1"
  extended_s3_configuration.0.bucket_arn:                   "" => "arn:aws:s3:::tf-test-bucket-72"
  extended_s3_configuration.0.buffer_interval:              "" => "300"
  extended_s3_configuration.0.buffer_size:                  "" => "5"
  extended_s3_configuration.0.cloudwatch_logging_options.#: "" => "<computed>"
  extended_s3_configuration.0.compression_format:           "" => "GZIP"
  extended_s3_configuration.0.prefix:                       "" => "tracking/autocomplete_stream/"
  extended_s3_configuration.0.role_arn:                     "" => "arn:aws:iam::187416307283:role/tf_acctest_firehose_delivery_role_72"
  name:                                                     "" => "tracking_autocomplete_stream"
  version_id:                                               "" => "<computed>"
aws_kinesis_firehose_delivery_stream.broken_tracking_autocomplete_stream: Still creating... (10s elapsed)
aws_kinesis_firehose_delivery_stream.broken_tracking_autocomplete_stream: Still creating... (2m0s elapsed)
aws_kinesis_firehose_delivery_stream.broken_tracking_autocomplete_stream: Still creating... (3m30s elapsed)
aws_kinesis_firehose_delivery_stream.broken_tracking_autocomplete_stream: Creation complete after 3m38s (ID: arn:aws:firehose:us-west-2:187416307283...erystream/tracking_autocomplete_stream)

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
```

Test Output:

```
terraform-provider-aws [b-aws-kfhd-crash-1657●] % acctests aws TestAccAWSKinesisFirehoseDeliveryStream_
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_s3basic
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_s3basic (142.95s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_s3WithCloudwatchLogging
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_s3WithCloudwatchLogging (153.92s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_s3ConfigUpdates
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_s3ConfigUpdates (266.77s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3basic
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3basic (282.11s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3InvalidProcessorType
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3InvalidProcessorType (2.86s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3InvalidParameterName
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3InvalidParameterName (2.49s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3Updates
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_ExtendedS3Updates (182.25s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_RedshiftConfigUpdates
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_RedshiftConfigUpdates (902.22s)
=== RUN   TestAccAWSKinesisFirehoseDeliveryStream_ElasticsearchConfigUpdates
--- PASS: TestAccAWSKinesisFirehoseDeliveryStream_ElasticsearchConfigUpdates (1236.74s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	3172.372s
```