Add host maintenance mode support for PowerVC Driver

As a cloud admin, it is able to set the host managed by PowerVC to
"maintenance mode" and disable the "maintenance mode" support, through
PowerVC Driver.
1. If set maintenance mode to "true" it responses: "on_maintenance"
2. If set maintenance mode to "false" it responses: "off_maintenance"
3. If set maintenance mode to "true" when the host is already in
maintenance mode, it will report the error message from PowerVC to user.

Change-Id: I59ef830244202a4337ad72292e6341406b8464d3
Closes-Bug: #1363912

common-powervc/powervc/common/client/extensions/nova.py

@@ -290,6 +290,16 @@ class PVCServerManager(servers.ServerManager):
         _resp, body = self.api.client.get(url)
         return body
 
+    def set_host_maintenance_mode(self, host, mode):
+        url = "/ego/prs/hypervisor_maintenance/%s" % host
+        if mode:
+            status = "enable"
+        else:
+            status = "disable"
+        body = {"status": status,
+                "migrate": "none"}
+        return self._update(url, body)
+
 
 class StorageConnectivityGroup(client_base.Resource):
     """

nova-powervc/powervc/nova/driver/virt/powervc/driver.py

@@ -1021,7 +1021,18 @@ class PowerVCDriver(driver.ComputeDriver):
         """Start/Stop host maintenance window. On start, it triggers
         guest VMs evacuation.
         """
-        raise NotImplementedError()
+        try:
+            self._service.set_host_maintenance_mode(host, mode)
+        except Exception as e:
+            # return powervc error message to uplayer
+            LOG.error(_("Set host maintenance mode failed: %s"), e)
+            return e.message
+        # return 'on_maintenance' or 'off_maintenance' string
+        # to nova-api response if pvc performed with no Exception
+        if mode:
+            return 'on_maintenance'
+        else:
+            return 'off_maintenance'
 
     def set_host_enabled(self, host, enabled):
         """Sets the specified host's ability to accept new instances."""

nova-powervc/powervc/nova/driver/virt/powervc/service.py

@@ -59,6 +59,10 @@ class PowerVCService(object):
         self.longrun_initial_delay = CONF.powervc.longrun_initial_delay
         # Add version checking as required
 
+    def set_host_maintenance_mode(self, host, mode):
+        resp = self._manager.set_host_maintenance_mode(host, mode)
+        return resp
+
     def list_instances(self):
         """Return the names of all the instances known to the virtualization
         layer, as a list.