Make test mysql connection code less confusing

There are two similar methods used for connecting to MySQL apps, but
their arguments differed in order which made for some confusion. This
makes their argument signatures identical.

Change-Id: I48818e2eadb81944e7369e12d09af9c3394d6b57
Adding override.config.template for percona

After the 'adding configuration group support' patch was merged,
percona instance-create is failing because the TM cannot find
the override.config.template for percona. Adding this template
fixes the problem.

Change-Id: I63404cfa8cd9bd850e4fc7457a3d4bcc2711685c
Closes-Bug: #1277376
Ignore outdated messages sent to conductor

Adds a sent_at field to conductor messages in the manager so that
messages that get out of sync on their way to conductor don't cause
trouble by updating instances or backups with out-of-date information.

Implements: blueprint conductor-ignore-old-messages
Change-Id: If06d2f9c9f993100be66f71274240a59b05b66e3
Merge "Make test mysql connection code less confusing"
Merge "Ignore outdated messages sent to conductor"