LU-13690 mdd: remove warnings in obd_lookup()

LU-13690 mdd: remove warnings in obd_lookup()

In obf_lookup() remove CWARN()s about invalid FID formats. Return
-ENOENT instead of -EINVAL for invalid FIDs. This removes noisy
console messages around volatile file handling in .lustre/fid/.

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Ia76f0da38baa86b8d1173cfe0ede52e275f68a28
Reviewed-on: https://review.whamcloud.com/38971
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>