Allow disabling tests with CATKIN_ENABLE_TESTING

[Smona]

Most ROS packages now allow disabling test runs by setting CATKIN_ENABLE_TESTING to false.

When I try to build laser_scan_matcher with CATKIN_ENABLE_TESTING set to false, I get this error:

CMake Error at /nix/store/y2dbjs0hpkdmra1jcnvih069nq27j9ka-ros-noetic-catkin-0.8.10-r1/share/catkin/cmake/test/tests.cmake:18 (message):
  () is not available when tests are not enabled.  The CMake code should only
  use it inside a conditional block which checks that testing is enabled:

  if(CATKIN_ENABLE_TESTING)

    (...)

  endif()

Call Stack (most recent call first):
  CMakeLists.txt:71 (add_rostest)

This PR just uses the recommended method to disable tests when the user requests it.

[130s]

• Making the test as an option makes sense to me. For developers' usecases they may not always want to run tests.
  • I found rostest.add_rostest is a very strict so that can be even more strong motivation to disable the tests.
• I just merged CI change #88 (it was opened a while ago but had been unmerged) into ros1 branch, the same branch this PR is aiming to. Would @Smona you mind enabling the tests in the CI config?

[130s]

Also do you mind @Smona cherry-picking the same changes into ros2 branch? Nevermind if you do.

[Smona]

Great, glad you are interested in merging this!

I've create a ros2 branch rebase of this in #91. I'm not sure what test configuration you're asking for, since my understanding is that CATKIN_ENABLE_TESTING is set to true by default.

[Smona]

@130s i've merged in the CI check, but I think you need to approve the run.

[130s]

Thanks for catching this up! Approving.
I'm not sure why CI has not run for this PR though, will see if it runs post-merge.