Write tests covering `dynamic_reconfigure` not found cases.

[artivis]

Write some unit tests to ensure the default behavior in case dynamic_reconfigure was not found during compilation (throwing etc).

[artivis]

Related #63, somewhat #62

[130s]

I might be misunderstood, but is this an attempt to capture import error when building .params files somewhat didn't go as expected so that the resulted files are not found during the application's runtime?

CC @malban

[artivis]

Hi @130s,
As you may know, rosparam_handler can be use with or without dynamic_reconfigure depending if it is found at compilation.
This particular ticket is actually about writing some unit test for the case where it is not found, making sure rosparam_hnadler behaves as expected (e.g. throws).