xfs/157: don't override SCRATCH_{,LOG,RT}DEV

xfs/157: don't override SCRATCH_{,LOG,RT}DEV

This tests wants to test various difference device configurations,
and does so by overriding SCRATCH_{,LOG,RT}DEV.  This has two downside:

 1) the actual SCRATCH_{,LOG,RT}DEV configuration is still injected by
    default, thus making the test dependent on that configuration
 2) the MKFS_OPTIONS might not actually be compatible with the
    configuration created

Fix this by open coding the mkfs, db, admin and repair calls and always
run them on the specific configuration.

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