test: allow LVM volumes or RAM disks as test devices

test: allow LVM volumes or RAM disks as test devices

Allow other device types for testing; this allows to test on
a larger variety of devices.

Option --dev=[loop|lvm|ram] selects loop device (default), lvm,
and ram disk, respecively. To use RAM disks with DDF,
the kernel parameter ramdisk_size=65536 must be used.
For LVM, use --volgroup=<vg> to specify the name of the volume
group in which the test LVs will be created.

Signed-off-by: Martin Wilck <mwilck@arcor.de>
Signed-off-by: NeilBrown <neilb@suse.de>