Added add_host plugin

- get ip address of the host bridge
- get pki certificate from engine guest
- add the host to the Default cluster
- added dependency on ovirt-engine-sdk

TODO: missing UX

Change-Id: I3b848643bc142144833142d1c2ff3a5625332443
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>