When VM is not started, vnc port value is -1 in the libvirt domain XML config.

Some tags were returning None because of bad decorator.

Support for registering/unregistering sub object to the cc-server.
Support for tag lifecycle handling (libev), was previously managed by plugins.

Try to connect to libvirt while no exception is thrown.

Clean global variable for libvirt connection.

No more global variable.

Create/Start/Stop/Destroy/Undefine/Export/Suspend/Resume.