features/index: Don't delete current xattrop index.

Problem:
`gluster v heal <volname> statistics heal-count` was not able to read the
number of entries to be healed from the source brick because the base xattrop
entries in indices/base_indices_holder and indices/xattrop were getting deleted
after a successful heal and the code flow prevented them from creating it again.

Fix:
Don't delete the xattrop index unless it is stale (i.e. brick is restarted)

Change-Id: Ief4eee0ddf42c4d8b711d00751be92bbbc7bbbb0
BUG: 1101647
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/7897
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>