storage: Adjust qemu-img switches check

storage: Adjust qemu-img switches check

Since we support QEMU 0.12 and later, checking for support of specific flags
added prior to that isn't necessary.

Thus start with the base of having the "-o options" available for the
qemu-img create option and then determine whether we have the compat
option for qcow2 files (which would be necessary up through qemu 2.0
where the default changes to compat 0.11).

Adjust test to no long check for NONE and FLAG options as well was removing
results of tests that would use that option.

Signed-off-by: John Ferlan <jferlan@redhat.com>