Make unit test run with catkin_make run_tests

[sloretz]

I notice the unit tests wasn't running when using catkin_make run_tests. I changed how the test was added to use the catkin cmake macros. I also added python-mock as a test dependency because the official ubuntu/trusty docker image does not have that installed by default.

[clalancette]

I love the change. However, it looks like all CI has failed, with no yaml. I think we'll need to add python-yaml to the package.xml as well.

[clalancette]

A couple of things:

• While you are messing around with the package.xml, it might be worthwhile to convert it over to format 2, to make it easier to integrate with ROS2.
• Travis is still failing, not being able to find urdf_parser_py. I've seen that locally when I forget to source devel/setup.bash in my catkin workspace; I think something similar must be going on with travis. Whether it is worthwhile to fix travis, however, I'm not sure.

[sloretz]

@clalancette Will do with the package.xml!

I learned from @dirk-thomas that unit tests can't expect to have the python path set up for importing python packages from the current package in all cases when using catkin_make. The unit test now adds ../src to sys.path. catkin_make_isolated and catkin build don't have this issue.

[sloretz]

@clalancette I updated the package.xml. An odd thing is it has a <depend>python</depend>. I'm 99% sure that is unnecessary.

[clalancette]

I agree with you that the on python is a bit weird. However, there are other packages (vision_opencv, for instance), which also have that dependency. I'll leave it up to you, but I'd just leave it in for now; it probably doesn't hurt anything. Otherwise, I think this looks good to me, so feel free to merge it.