add more test cases to improve the test code coverage #5

In this patch, the following module test coverage improved to 100%

ceilometer/alarm/partition/coordination

Class PartitionIdentity was not tested for various method. This
patch set correct that problem. Also, class PartitionCoordinator
has 3 exception branches were not tested. This patch set added
more test cases to check these conditions.

Change-Id: Ia33a28e1650b6312843375af04973c9d5da2d89d
Merge "add more test cases to improve the test code coverage #5"