Change waiting on mariadb.pid
Change waiting on mariadb.pid

Previously the code looked at mariadb.pid, but this seemed
flakey in function.  It seemed racey and prone to failure on
slower connections to a registry.  The original task was
extremely complex and it didnt really verify that the MariaDB
was ready to serve connections.  Use wait_for with a regex
instead.

Change-Id: I3aafac04f03639b08e0ef4d6a9c9e1a4499f000c
Closes-Bug: #1564278

tonyli71/kolla,stackforge/kolla,mrangana/kolla,openstack/kolla,nihilifer/kolla,coolsvap/kolla,rahulunair/kolla,dardelean/kolla-ansible,mandre/kolla,stackforge/kolla,openstack/kolla,rahulunair/kolla,nihilifer/kolla,coolsvap/kolla,intel-onp/kolla,tonyli71/kolla,mrangana/kolla,coolsvap/kolla,mandre/kolla,dardelean/kolla-ansible,mandre/kolla,GalenMa/kolla,dardelean/kolla-ansible,intel-onp/kolla,stackforge/kolla,GalenMa/kolla