Fix the pool client auth test

There was an intermittent test failure in the
test_pool_reencryption_client_authentication test where members are detected
as unbalanced. This was due to the time it takes for the health monitor to
bring the member back into the pool.
This change adds a waiter for the members to go operating_status ONLINE before
checking for balanced member requests.

Story: 2010660
Task: 47710
Change-Id: Ibb1f351c77f3ed7a0c69c8295973f77ab2069dad
1 file changed