Add new version of stopUser performance test

Similar to what was done for switchUser, this commit adds a new version
of the stopUser test. In this variation, a single user is created per
test run (instead of one per iteration of the run) and a wait for cool
down was added in between iterations.

Bug: 261621873
Test: atest UserLifecycleTests#stopUser_realistic
Change-Id: Ief41deeea82392e6d44ff5520acffebfcc53f69d