Correct ros dependencies with gazebo plugins

[Jaeyoung-Lim]

Problem Description The NO_ROS cmake option was broken, since plugins that were being built with the NO_ROS option had ros depdendencies.

Solution This PR corrects the NO_ROS option so that plugins that depend on ROS does not get built. It seems like it is basically most of them.

This allows us to build the gazebo_mavlink_interface and use the mavlink inside PX4 in order to verify mavlink compatibility with rotorS mavlink implementation

The ROS dependency seems to be added in https://github.com/ethz-asl/rotors_simulator/pull/328

Additional Context

• Fixes https://github.com/ethz-asl/rotors_simulator/issues/660

[Jaeyoung-Lim]

@michaelpantic Thanks!