vdsm: add console device to the VM

Add console device to the Hosted Engine VM definition.
Allows to connect to the VM without X.

Change-Id: Ieabe9538571a6e4e18217a728c71677225b1fddb
Bug-Url: https://bugzilla.redhat.com/1001706
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>