Finish configuring service before starting haproxy for it

Starting an HAProxy instance for ceilometer-api will fail on Ubuntu if
the package for service is installed but not yet configured, because the
service is still running in its default configuration binding to 0.0.0.0
instead of just the management IP, preventing HAProxy from binding to
the management VIP.

To prevent a dependency loop (Ceilometer, like most other OpenStack
services, depends on MySQL), Galera dependency on the whole of HAProxy
has to be narrowed down to just the MySQL parts.

Change-Id: I5fa03dbc3f7e3a7dfa57c226a5396f652c111997
Closes-bug: #1264388