Improve logging and raising DiskFileNoSpace

This commit only improves logging whenever ENOSPC (No space on disk)
or EDQUOT (Quota limit exceeded) is returned by glusterfs

Also, added methods to:
- get filename from file descriptor
- log with rate limit

Caveat: Although raising DiskFileNoSpace results in object-server
returning HTTPInsufficientStorage[507] correctly, the swift proxy-server
invokes "best_response" method that returns [503] to the user.

When write-behind translator is turned on in glusterfs, it may set
errno to EIO instead of ENOSPC/EDQUOT. This is documented in BZ 986812

BUG: 985862, 985253, 1020724
Change-Id: Ib0c5e41c11a8cdccc2077f71c31d8a23229452bb
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/6199
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>
Reviewed-on: http://review.gluster.org/6269