tests: qemublock: Test handling of all cache modes

tests: qemublock: Test handling of all cache modes

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

dir-fat-cache.xml:
-drive file=fat:/var/somefiles,if=none,id=drive-dummy,readonly=on,cache=directsync
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=off

file-backing_basic-cache-directsync.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow2,if=none,id=drive-dummy,cache=directsync
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=off

file-backing_basic-cache-none.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow2,if=none,id=drive-dummy,cache=none
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=on

file-backing_basic-cache-unsafe.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow2,if=none,id=drive-dummy,cache=unsafe
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=on

file-backing_basic-cache-writeback.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow2,if=none,id=drive-dummy,cache=writeback
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=on

file-backing_basic-cache-writethrough.xml:
-drive file=/var/lib/libvirt/images/a,format=qcow2,if=none,id=drive-dummy,cache=writethrough
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=off

network-qcow2-backing-chain-cache-unsafe.xml:
-drive file=rbd:rbdpool/rbdimg:id=testuser-rbd:auth_supported=cephx\;none:
        mon_host=host1.example.com\;host2.example.com,
        file.password-secret=node-a-s-secalias,format=qcow2,
        if=none,id=drive-dummy,cache=directsync
-device virtio-blk-pci,scsi=off,drive=drive-dummy,id=dummy,write-cache=off

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