Fix build failure in usermanager.implementation

ISSUE:
Current usermanager.implementation junit code assumes test functions are run in order.
There is a add function and then a remove function to add/remove an object from a map.
In some machines consistently the remove function is invoked by junit first.
This leads to a failure/succes/failure/success... pattern for usermanager.implementation
builds.

Change-Id: Ie5041c6980f9dad0aeb1f11a27c0c3e9bab9dbcf
Signed-off-by: Alessandro Boch <aboch@cisco.com>