Remove path_exists from NFS/GlusterFS drivers

mkdir -p will not throw an error if the path already exists,
so this method is unneeded in these classes.

Change-Id: I65a67cb75f83f65a6f80c7a90f77c2c5133bd41b
Merge "Remove path_exists from NFS/GlusterFS drivers"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp