ext4/306: avoid failures caused by incompatible mount options

ext4/306: avoid failures caused by incompatible mount options

ext4/306 will fail when mounting the ext3 file system it creates if an
ext3-incompatible mount option is applied by _scratch_mount.  This can
happen if EXT_MOUNT_OPTIONS is defined appropriately in the test
environment.  For example, the block_validity option is commonly used
to enhance ext4 testing, and it is not supported by ext3.

Fix this by instead creating an ext4 file system without extents as a
functionally equivalent substitute.  This will also eliminate a
dependency for ext3 support on the test system.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>