cluster/afr: Fix xattr heal comparison checks

        Backport of part of the fixes in http://review.gluster.org/8558

Problem:
While implementing list-xattr based meta-data self-heal for afr-v2 we found
2 issues, with afr-v1's implementation.

1) change in QUOTA_SIZE_KEY xattr value can trigger spurious  metadata
   self-heal.
2) xattr comparison function that is implemented for afr-v1 checks if the
   number of xattrs in both the xattrs is same and then checks that the xattrs
   present in brick-1's response are present and equal. But what we observed me
   was that count also contains the gluster internal/virtual xattrs where as
   the compare function should only compare on-disk external xattrs that can be
   healed. So the correct implementation should check that the external xattrs
   in first brick's response are present in second brick's response and vide
   versa.

Fix:
This patch is partly backported from afr-v2's implementation. Will be providing
the links where necessary.

1) Added QUOTA_SIZE_KEY xattr to the list of xattrs that need to be ignored.
   (http://review.gluster.org/#/c/8558/10/xlators/cluster/afr/src/afr-common.c
   line: 1155)
2) For xattrs to be equal, check all keys in xattr-dict1 are in xattr-dict2 and
   equal and vice versa.
   (http://review.gluster.org/#/c/8558/10/xlators/cluster/afr/src/afr-common.c
   line: 1195)

Change-Id: I63aa74858c6f608b98d1fe425b3fa56f925bb5b3
BUG: 1162230
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/9090
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>