Use timeutils.utcnow in alarm threshold evaluation

This change use timeutils.utcnow() in alarm threshold evaluation
instead of datetime.utcnow() to allow mock the the now datetime

It also add a test to check the behavior of bound_duration method.

Change-Id: I970e63da33e17018ed4fef31d0082803f6e0fb29
Merge "Use timeutils.utcnow in alarm threshold evaluation"