init commit
removed xtradb_wsrep_cluster_addresses var since this is determined during runtime
Merge xtradb's directory structure into this one.
Update paths in top-level percona playbook.

To match directory structure in this tree.
Make a few tweaks to percona role:

- remove unnecessary apt-key and apt-repo presence checks.
    ( the apt_key and apt_repo modules are idempotent )

- put apt-repo inline with apt_repo module, instead of template file.

- don't show red output when testing for my.conf existence, by
  `test`-ing for the file, so it always exits 0.

- nest vars under xtradb/mysql hash keys.

- remove apparmor disable stuff, to avoid red error output, since
  apparmor mysqld profile doesn't seem to exist on any of my ubuntu
  12.04 test machines/vms.