LU-1301 helpers: quiet class_parse_nid()

LU-1301 helpers: quiet class_parse_nid()

class_parse_nid_quiet() is a version of class_parse_nid()
which doesn't complain on an invalid nid.
i.e. used in obd_mount.c where nid can be followed by
another (non-nid) mount option.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I8938a50e56007bd626b207e4a69a2a76c572632d
Reviewed-on: http://review.whamcloud.com/3678
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <tappro@whamcloud.com>