Merge branch 'release-1.3.15' into develop

* release-1.3.15: (27 commits)
  Bumping version to 1.3.15
  Update changelog to the latest version
  EMR: Bug fixes:Fixed describe-cluster to support pagination.
  EMR: Modified create-cluster and add-instance-groups output.
  Disable preview plugin when running EMR tests
  EMR: Updated help message and examples.
  EMR: Support mixed case in InstanceGroupType in create-cluster and add-instance-groups
  EMR: Set create-cluster --ami-version as a required option and add regex check. Updated help text. Updated create-cluster unit tests.
  EMR: Modified describe-cluster to fetch all results. Used FROM_FILE to read example files for EMR commands. Fixed unit tests.
  EMR: Updated help texts and examples.
  EMR: Minor code restructure. Refactored helper methods, add-tags and create-default-roles.
  EMR: Made changes required for Python 2.6 and 3.3 in Mac OS. Fixed bugs in ssh.py
  EMR: Fixed unit tests and formatting.
  EMR: Adds Properties field for --steps option.
  EMR: Add tests for reading custom argument schema input from json.
  EMR: Added validation for applications.
  EMR: Fix putty key file format bug.Add feature to use executable based on key format if both ssh and putty are available.
  EMR: Updated  help text.
  EMR: Implemented create-cluster, add-steps, add-tags, create-default-roles, create-hbase-backup, disable-hbase-backup, schedule-hbase-backup, add-instacne-groups, ssh, socks, put, get, install-applications commands. Refactored describe-cluster. Added unit tests and examples.
  EMR: Added constants; Fixed minor typo in add-tags command.
  ...
Add thread id to debug logs

Makes it easier to troubleshoot S3 debug logs.
Merge branch 'add-thread-id' into develop

* add-thread-id:
  Add thread id to debug logs
Update changelog with latest bug fixes
Bumping version to 1.3.16
Merge branch 'release-1.3.16'

* release-1.3.16:
  Bumping version to 1.3.16
  Update changelog with latest bug fixes
  Add thread id to debug logs