Coverage reporting and test suite integration

Integrate the test-suite and use it for generating a coverage report.

Goals:

• test-suite runs automatically by CMake
• test-suite is instrumented with coverage generation
• coverage information generated during test-suite run is collected
• coverage information made accessible via codecov.io / download / other means

Related to #7 (closed) and #8

Current status: Coverage information is pushed to codecov.io at https://codecov.io/gl/musteresel/rodos/branch/coverage

Main issue: Code coverage generation is wrong! For example core-fast/helloworld-minimalistic.cpp is shown as not covered even though it ran during the build which generated this coverage information. Unfortunately I've currently no idea how to fix / change this. seems to work now

Also todo: Generate / merge coverage reports for more than one port: Currently only posix is run, but linux-x86 and linux-makecontext can also be run. The coverage information of all three should be merged. done