[TASK] Fix intermittent failures in SessionTest

At time the garbageCollectionOnlyRemovesTheDefinedMaximumNumberOfSessions
in SessionTest fails with "Failed asserting that 1 matches expected 5."

Since the test is about making sure a maximum is not exceeded, this
changes the assertion from "equal" to "less than or equal".

Change-Id: I87c6d38dd3ddd7a4c5db838584a7249659fbac27
Releases: master, 2.2, 2.1