Explicitly specify mysql node address

If node address is not explicitly specified, mysql galera may sometimes
use virtual IP as "source" IP when joining to cluster. It fails because this
virtual IP is not on list of IPs of cluster nodes (wsrep_cluster_address).

Change-Id: Iec08a458c747f4415a961022c56f66fe0a1f60b4
MySQL Element: Make userhandle an optional paramater

This updates the code to reflect the README.md documentation

Change-Id: Ia5cbb7b4a3caf59f47b7c6fb259c964989f1d0d4
Enable collectl on systemd OSes.

We now ensure that the collectl systemd service is enabled on OSes that
require such things.

Change-Id: I5186fb7abf8706f198ff10ced3e245b871edb2a1
Merge "MySQL Element: Make userhandle an optional paramater"
Merge "Enable collectl on systemd OSes."
Merge "Explicitly specify mysql node address"