xfs_scrub_all: escape service names consistently

xfs_scrub_all: escape service names consistently

This program is not consistent as to whether or not it escapes the
pathname that is being used as the xfs_scrub service instance name.
Fix it to be consistent, and to fall back to direct invocation if
escaping doesn't work.  The escaping itself is also broken, but we'll
fix that in the next patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>