LU-11156 scrub: skip project quota inode

Error happened when scrub try to process project quota inode.
Scrub thinks that it is IGIF, because it has no lma fid. And it starts
to create O/inum/{LAST_ID,d0-d31}, and fails with not enough credits.
The project quota inode s_prj_quota_inum should be skipped
from scrub iteration.

Signed-off-by: Alexander Boyko <c17825@cray.com>
Cray-bug-id: LUS-6197
Change-Id: I38c347377a1c648ac3dd3e3ff4c4d65ee34cde39
Reviewed-on: https://review.whamcloud.com/32829
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>