env_process: mv creating of vm into libvirt specific block.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
These two lines are also related with vm_type. Maybe you can put them into 'if vm_type == 'libvirt'' branch. And if the connect_uri is changed just set the vm to None. And we can still use 'if not vm' in following code. :)