qemu.tests.cfg.qemu_img: minor update for configure.

Correct image_cluster_size to cluster_size under convert test.
RHEL.5 host do not support qed

Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.qemu_vm: Check available before send cmdline to monitor in spice migration code

Also add default for cmdline

Without this patch, code may fail on rhel5 host.

Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.qemu_vm: Indent fix in spice related code

Signed-off-by: Feng Yang <fyang@redhat.com>