Add test cases

[onitake]

restreamer needs automated tests.

Non-exhaustive list, also consider combinations:

• Network simulation (congestion, drops, ...)
• Correct timing (scan PTS)
• Buffer contention (check memory usage)
• Stream drops (disconnects, lack of data, broken data)
• Multiple upstreams

[onitake]

Some unit tests have been added, but they are not complete and system tests are still needed.