Adding option in run to accept s3_conn_id

[msumit]

Targeting 2 things in this PR:

1. Ability to specify a s3_conn_id from cli
   airflow run -s3 s3_default example_python_operator print_the_context 2016-01-07
2. Using calling format in boto, so it doesn't throw ssl exceptions for buckets which have dots in their name.

[jlowin]

@msumit I believe this is superseded by #1137 which lets users specify the hook that should be used for remote logging (for example, a specific S3 hook). That should take care of your first issue. If the second issue is still a problem, could you please add a PR to S3Hook directly?

[landscape-bot]

Code quality remained the same when pulling 24841ed on msumit:s3_conn into 71f99f8 on airbnb:master.