iotests/block-status-cache: New test

iotests/block-status-cache: New test

Add a new test to verify that want_zero=false block-status calls do not
pollute the block-status cache for want_zero=true calls.

We check want_zero=true calls and their results using `qemu-img map`
(over NBD), and want_zero=false calls also using `qemu-img map` over
NBD, but using the qemu:allocation-depth context.

(This test case cannot be integrated into nbd-qemu-allocation, because
that is a qcow2 test, and this is a raw test.)

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220118170000.49423-3-hreitz@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>