Adding support to backup to Glusterfs

Added a new backend class (i.e., GlusterBackend) and made
a few fixes to support other backup destination besides
S3/Glacier/Swift

Signed-off-by: Thiago da Silva <thiagodasilva@gmail.com>
Merge branch 'adding_gluster_backend' of https://github.com/thiagol11/bakthat into adding_gluster_backend

Conflicts:
	bakthat/backends.py