Release Notes - Apache Twill - Version 0.12.1

Improvement
[TWILL-251] - Hadoop21YarnNMClient logs too frequent on stopping container

Bug
[TWILL-61] - Second launch attempt of AM always failed
[TWILL-254] - Update to use ContainerId.fromString in Hadoop 2.6+
[TWILL-255] - Incorrect logging after memory/cpu was adjusted