avocado.utils.params: Add copy() method
avocado.virt.qemu.devices: Add QemuDevices.clone() method

Create a virtual machine and copy the devices added to
it so far. This is important to implement migration.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt.machine: Add migrate method

In order to test live migration, introduce a migrate()
method to the QEMU VM class.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
tests/qemu: Add QEMU live migration test

This showcases how a QEMU live migration test looks in
avocado.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>