Fixed bug in __str__ and __add__ overload operators for bandit SampleArm and HistoricalData.
Added tests for SampleArm.__add__
Fixed SampleArm.__add_. Now returns a new SampleArm, does not modify original arm. Also added more tests.
use deepcopy to copy historical_info for testing so it does not modify the test case.
Added checking that the arm given to SampleArm.__add__ is a SampleArm.
Merge branch 'master' of https://github.com/Yelp/MOE into norases_387_fix_bandit_bugs_and_add_new_tests
Updated ValueError comment for SampleArm.__add__
Reverted isinstance check for SampleArm.__add__
Added __iadd__ and __radd__ to SampleArm.
Validate SampleArm.__iadd__ and added a test for it.
Fixed Eric's comments and updated SampleArm.__iadd__ test.
Fixed docstring too long and assertion too long in SampleArm tests.
Updated CHANGELOG.
Merge pull request #389 from Yelp/norases_387_fix_bandit_bugs_and_add_new_tests

Fixed str and add bugs in bandit data containers