virt: 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 connect function into virsh module.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virt: Add a utils_conn module in virttest.

Well, there are so many transport type in remote uri.
So I think that making a module to hanle all kinds of
connection is a good idea.This module is not completed
but just contain tls transport in this commit.
Other transport will be completed in future if utils_conn
is also a good idea to others.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
virt: add configuration and test module for virsh connect.

Add virsh_connect.cfg into libvirt/tests/cfg.
And add virsh_connect.py into libvirt/tests.

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