Fix role build failures in certain OSes and OS versions

[geerlingguy]

Current status:

• CentOS 6
• CentOS 7
• Ubuntu 12.04
• Ubuntu 14.04

See: https://travis-ci.org/geerlingguy/ansible-role-glusterfs

[geerlingguy]

For 12.04, it's weird... seems that the package isn't available, but it should be: http://packages.ubuntu.com/search?keywords=glusterfs-server

For 14.04, for some reason the server isn't starting in the container... so I may have to switch to manual and futz around some locally in my test VM.

[geerlingguy]

Note that the official docs recommend using Gluster's PPA for Ubuntu (don't know if it's been updated for xenial yet): http://www.gluster.org/community/documentation/index.php/Getting_started_install — that's something to consider...