GlusterFS - client support without using plugins

[cbmckni]

Development of a SciApp requires standalone Docker images that do not depend on any plugins. The current usage of GFS plugins for mounting volumes is being addressed in two ways:

1. A NFS Mount Option - see nfs-in-docker

2. A GFS mount option - Installing the GFS Native Client to head node and workers. Development is located in the gfs-no-plugins branch.

A comparison between using NFS and the GFS Client to mount GFS volumes can be found in the documentation:
The GFS Client performance is slightly slower than the NFS method based on tests, but not drastically so. The gain is automatic HA client failover, which is typically worth the effect on performance.