virttest.virsh: Add a parameter for VirshSession to make remote session clear.

With original logic of VirshSession.__init__(), we have
not choice but configuring auto-ssh-login for "local to
remote: virsh -c uri".
While for other types driver like esx, it will fail.
Now support login with password if auto-ssh-login is impossible.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libvirt.tests: Fix bug for remote testcase of vcpuinfo.

The parameter "connect_uri" will effect vm's connect_uri.
But it is not useful in remote testcases because what we
need is remote_connect_uri which means connection from
remote to local.
And it shouldn't replace connect_uri of libvirt_vm, otherwise
all operation to local vms will need authorization.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>