common/xfs: use whole-word matching for _require_xfsrestore_xflag

common/xfs: use whole-word matching for _require_xfsrestore_xflag

On my system, the path to the xfsrestore binary is:

/code/xfsdump/build-x86_64/restore/xfsrestore

The grep command in _require_xfsrestore_xflag matches on the "build-x86"
part, even though my version of xfsrestore does not actually have a -x
flag.  Fix the string parsing to match entire words so that we only look
for -x in the help output.

(Maybe someone should patch xfsrestore -h to report basename(argv[0])
instead of argv[0]...)

Fixes: 1ffa16c573 ("xfs: test for fixing wrong root inode number in dump")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>