Add new gnmi-standalone driver with fake mastership handling

gNMI does not support mastership. This driver allows controlling gNMI
devices without the need of other mastership-oriented protocols (e.g.
P4Runtime).

Change-Id: I300607fbcc99d3f066904a96e55c9cd954d5d0a5
diff --git a/drivers/gnmi/src/main/resources/gnmi-drivers.xml b/drivers/gnmi/src/main/resources/gnmi-drivers.xml
index 0928284..3204aed 100644
--- a/drivers/gnmi/src/main/resources/gnmi-drivers.xml
+++ b/drivers/gnmi/src/main/resources/gnmi-drivers.xml
@@ -15,7 +15,7 @@
   ~ limitations under the License.
   -->
 <drivers>
-    <driver name="gnmi" manufacturer="gnmi" hwVersion="master" swVersion="master">
+    <driver name="gnmi" manufacturer="Unknown" hwVersion="Unknown" swVersion="Unknown">
         <behaviour api="org.onosproject.net.device.DeviceDescriptionDiscovery"
                    impl="org.onosproject.drivers.gnmi.OpenConfigGnmiDeviceDescriptionDiscovery"/>
         <behaviour api="org.onosproject.net.device.DeviceHandshaker"
@@ -25,5 +25,11 @@
         <behaviour api="org.onosproject.net.behaviour.PortAdmin"
                    impl="org.onosproject.drivers.gnmi.OpenConfigGnmiPortAdminBehaviour"/>
     </driver>
+
+    <driver name="gnmi-standalone" manufacturer="Unknown" hwVersion="Unknown"
+            swVersion="Unknown" extends="gnmi">
+        <behaviour api="org.onosproject.net.device.DeviceHandshaker"
+                   impl="org.onosproject.drivers.gnmi.GnmiHandshakerStandalone"/>
+    </driver>
 </drivers>