This commit implements support for Ubuntu 16.04 Xenial. Changes
include renaming several variables from galera_* to percona_* for
clarity. The reason for this change is that 16.04 will be using
distribution provided packages for percona-xtrabackup.
Mariadb 10.0 packages are available for Ubuntu 16.04, so those
packages and installations procedures will remain unchanged.
Depends-On: Iab5485529cf14933fd7f37430d234a5c41185c18
Change-Id: I4baeb2eddf137619ffedba2f9efd61b7bd142f92
5136160186