Better tests for Raspberry Pi

[Razican]

Currently tests work to be built in Travis CI. Nevertheless, since in Travis they do not have the hardware of the Raspberry Pi, some more tests use the camera on-board the Raspberry Pi if available. This is great, but it should also be applied to the GPS, GSM and even Serial tests, not to mention the future temperature and XBee tests.

[Razican]

This is going to be implemented on the rust version. Maybe we could backport those tests, even though it means to modify some constants to check if we are on the raspberry pi. Maybe we could put flags as we did with with different compilation schemes. Constants such as GSM_CHECK or GPS_CHECK to actually check the components themselves.