mysql55 package name update to mysql55u with service state maintained.

This is an example based on what I emailed Ben about in order to make IUS package keep mysqld running after a Obsolete upgrade to mysql55u.

I couldn't work out a better way of storing the running status of the service, as environmental variables didn't appear to persist between the triggerun and triggerpostun events.

The interaction is different to a normal upgrade's condrestart, but both follow the same sequence:

* check if running
* stop the old server
* start the new server

I've tested this for both scenarios of mysqld not running, and mysqld running on CentOS 5 and 6 using Webtatic, though not done this with your IUS ones.

I don't expect this to be merged, more just a talking point.