We should allow testing this on tmpfs. Any cache setting in iotests
should try to obey $CACHEMODE.

The cache mode is still "none" by default but overridable
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

This is an initial, simple live migration test from one
running VM to another, using monitor commands.

This is also an example of using the new common.qemu functions
for controlling multiple running qemu instances, for tests that
need a live qemu vm.
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NJeff Cody <jcody@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>