We have two leftover "capabilites" for qemu-img:
QEMU_IMG_BACKING_FORMAT_OPTIONS
QEMU_IMG_BACKING_FORMAT_OPTIONS_COMPAT

The former says we are able to specify the backing format via -o
(which has been the case for a long time now) and the second one
says we can use -o compat to specify the qcow2 version.

Since we require QEMU 1.5.0, we can always assume -o compat,
which was introduced in QEMU 1.1.

Drop the test cases using FMT_OPTIONS which have a FMT_COMPAT
counterpart to prepare for deprecating FMT_OPTIONS (and these flags)
completely.
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>