webadmin: Fixing infinent loop in NewGuideVmInterfaceModel.

Fix for the static invocation of NewGuideVmInterfaceModel.createInstance
from the same method, which causes an infinent loop.

Change-Id: I94b0db601a0b88b8083eabd5e285bdb1b3168d38
Signed-off-by: Asaf Shakarchi <asaf@redhat.com>