provider/aws: Add 'aws_iam_account_alias' data source

[ewbankkit]

Returns the IAM account alias for the AWS account associated with the provider connection.
I though about adding this functionality to the aws_caller_identity data source but since it makes a call to the IAM service there could be an issue with permissions (e.g. not authorized to call that service or operation) and didn't want to break backwards compatibility.
Acceptance tests:

make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSIamAccountAlias_'

[stack72]

Hi @ewbankkit

Thanks for the work here - I resolved the merge conflicts and the tests pass as expected:

% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSIamAccountAlias_basic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/12/18 14:11:21 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSIamAccountAlias_basic -timeout 120m
=== RUN   TestAccAWSIamAccountAlias_basic
--- PASS: TestAccAWSIamAccountAlias_basic (13.79s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	13.845s

Paul

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