qemu.tests: Add block resize case

Add a case for block resize. Use monitor command to resize the block
device. And check it inside guest. This case support Windows and
Linux, qcow2 and raw, virtio_blk, virtio_scsi and ide with different
parameters.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #492 from ypu/block_resize

qemu.tests: Add block resize case