Problem with GlusterFS #748

Hi.

I just fought with DiskSpaceCollector because it didn't report the disk usage for a fuse.glusterfs mounted directory.

The first problem (trivial) was that in the default config "gluster" is given instead of "fuse.gluster" . No problem, corrected.

But even after correction the metrics were silently dropped.
I found that the if at diskspace.py:153 assumes the "device" starts with a '/'. Too bad, usually mountpoints for gluster use the format
srv1[,srv2]:volume_name

It's possible to use
/srv1[,srv2]:volume_name
(with a leading '/') but I think it's quite uncommon.
I made that if a no-op (adding as first condition "(1==1) or" ), but I think it could be better to consider the GlusterFS case and/or give a meaningful message stating why that mountpoint is getting discarded.

HIH