virttest-virsh: fix prompt in VirshSession to support prompt 'virsh >'

When connect --readonly in a virsh session, the prompt changes to 'virsh >'.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virt: add method 'get_uri_with_transport' into libvirt_vm.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virttest.virsh: Add connect function for virsh module.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>