message: backend: add missing override keyword to action
diff: @@ -13,7 +13,7 @@ public:
  grpc::Status Arm(grpc::ServerContext * /* context */,
  const dronecore::rpc::action::ArmRequest * /* request */,
  - dronecore::rpc::action::ArmResponse *response)
  + dronecore::rpc::action::ArmResponse *response) override
  {
  auto action_result = _action.arm();
  @@ -38,7 +38,7 @@ public:
  grpc::Status Disarm(grpc::ServerContext * /* context */,
  const dronecore::rpc::action::DisarmRequest * /* request */,
  - dronecore::rpc::action::DisarmResponse *response)
  + dronecore::rpc::action::DisarmResponse *response) override
  {
  auto action_result = _action.disarm();
  @@ -51,7 +51,7 @@ public:
  grpc::Status Takeoff(grpc::ServerContext * /* context */,
  const dronecore::rpc::action::TakeoffRequest * /* request */,
  - dronecore::rpc::action::TakeoffResponse *response)
  + dronecore::rpc::action::TakeoffResponse *response) override
  {
  auto action_result = _action.takeoff();
  @@ -64,7 +64,7 @@ public:
  grpc::Status Land(grpc::ServerContext * /* context */,
  const dronecore::rpc::action::LandRequest * /* request */,
  - dronecore::rpc::action::LandResponse *response)
  + dronecore::rpc::action::LandResponse *response) override
  {
  auto action_result = _action.land();
  @@ -77,7 +77,7 @@ public:
  grpc::Status Kill(grpc::ServerContext * /* context */,
  const dronecore::rpc::action::KillRequest * /* request */,
  - dronecore::rpc::action::KillResponse *response)
  + dronecore::rpc::action::KillResponse *response) override
  {
  auto action_result = _action.kill();
  