iotests.py: qemu_img*("create"): support IMGOPTS='compression_type=zstd'

iotests.py: qemu_img*("create"): support IMGOPTS='compression_type=zstd'

Adding support of IMGOPTS (like in bash tests) allows user to pass a
lot of different options. Still, some may require additional logic.

Now we want compression_type option, so add some smart logic around it:
ignore compression_type=zstd in IMGOPTS, if test want qcow2 in
compatibility mode. As well, ignore compression_type for non-qcow2
formats.

Note that we may instead add support only to qemu_img_create(), but
that works bad:

1. We'll have to update a lot of tests to use qemu_img_create instead
   of qemu_img('create'). (still, we may want do it anyway, but no
   reason to create a dependancy between task of supporting IMGOPTS and
   updating a lot of tests)

2. Some tests use qemu_img_pipe('create', ..) - even more work on
   updating

3. Even if we update all tests to go through qemu_img_create, we'll
   need a way to avoid creating new tests using qemu_img*('create') -
   add assertions.. That doesn't seem good.

So, let's add support of IMGOPTS to most generic
qemu_img_pipe_and_status().

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20211223160144.1097696-5-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>