ALLJOYN-2461 Fixed race condition bug in the SessionListenerTest

The session listener flags should be reset before the second client joins the
service.  If it is not cleared it will contain the information from the first
client.  Since the session_member_added_flag is set on a separate thread we
must also wait for that flag in addition to the other flags we are already
waiting for.

Change-Id: I570387a609d838225a9da5132ec5bfaf7078040e