Re-enable percona-cluster for ppc64el when Xenial percona-cluster bugs are fix-released

[ryan-beisner]

This issue is a reminder that when the following bugs are resolved, we need to re-validate with percona-cluster and remove the mysql charm work-around. It should also be possible to remove the bundle-ppc64el.yaml file and update the docs to just use bundle.yaml for both ppc64el and amd64.

Temporarily substituting the mysql charm for percona-cluster, pending
resolution of the following bugs.  Also, there is no Xenial mysql
charm as of 2016 Aug 8.
    https://bugs.launchpad.net/percona-xtradb-cluster/+bug/1570678
    https://bugs.launchpad.net/charms/+source/percona-cluster/+bug/1611134

https://github.com/openstack-charmers/openstack-on-lxd/blob/master/bundle-ppc64el.yaml

[AeroLoongLab]

Hey ryan,
Looks like that the following defect also blocks enablIng persona-cluster for ppc64el.
https://bugs.launchpad.net/ubuntu/+source/galera-3/+bug/1606102

logs:
2016-09-26 05:42:45 2203 [ERROR] WSREP: galerautils/src/gu_init.c:gu_init():20: GU_PAGE_SIZE(4096) does not maptch real system page size(65536)