virt: Multihost Cpuflags migration cpu on off

This test adds test which migrate guest with turned off cpu.

1) boot guest on source host
2) disable cpu disable_cpus = "1 2"
3) migrate to destination host
4) check guest if all disabled cpu are still disabled after migration.
*) switch source and dest and repeat migrate migrate_count times.

Signed-off-by: Jiří Župka <jzupka@redhat.com>