Peripheral changes for networks

Specifically:
 * export a new environment variable for the gnt-os-interface
 * export a new environment variable for KVM specific scripts
 * ovf support for networks

Signed-off-by: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Reviewed-by: Iustin Pop <iustin@google.com>