iotests: add tests for "qemu-img rebase" with compression

The test cases considered so far:

314 (new test suite):

1. Check that compression mode isn't compatible with "-f raw" (raw
format doesn

iotests: add tests for "qemu-img rebase" with compression

The test cases considered so far:

314 (new test suite):

1. Check that compression mode isn't compatible with "-f raw" (raw
format doesn't support compression).
2. Check that rebasing an image onto no backing file preserves the data
and writes the copied clusters actually compressed.
3. Same as 2, but with a raw backing file (i.e. the clusters copied from the
backing are originally uncompressed -- we check they end up compressed
after being merged).
4. Remove a single delta from a backing chain, perform the same checks
as in 2.
5. Check that even when backing and overlay are initially uncompressed,
copied clusters end up compressed when rebase with compression is
performed.

271:

1. Check that when target image has subclusters, rebase with compression
will make an entire cluster containing the written subcluster
compressed.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20230919165804.439110-9-andrey.drobyshev@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

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