Added test_interface_files repo for test_msgs

[wilcobonestroo]

Added test_interface_files repo to make the test_msgs build in dashing.

[jacobperron]

I think this shouldn't be necessary since we can rely on the upstream version installed on the system. For example on Linux, test_interfaces_files should be installed with rosdep, or manually with sudo apt install ros-dashing-test-interface-files