tests: qemublock: Test handling of 'unmap' and 'detect-zeroes' options

tests: qemublock: Test handling of 'unmap' and 'detect-zeroes' options

The test cases would correspond to the following -drive command lines:

file-backing_basic-detect.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow,if=none,id=drive-dummy,detect-zeroes=on
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy

file-backing_basic-unmap-detect.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow,if=none,id=drive-dummy,discard=unmap,detect-zeroes=unmap
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy

file-backing_basic-unmap-ignore.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow,if=none,id=drive-dummy,discard=ignore,detect-zeroes=on
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy

file-backing_basic-unmap.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow,if=none,id=drive-dummy,discard=unmap
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>