Attempt to make test_memcache_pool_timeout stable

Too much time can pass after we create a set of co-routines and when
the parent co-routine continues is setup and staging. Instead, we
perform all the setup and staging, let the system run and then verify
the final state after all the dust settles.

Change-Id: I801148e380807119d3d6da5a24ba9cced39fb339
Closes-Bug: 1272503
Merge "Attempt to make test_memcache_pool_timeout stable"