Work around python bash completion bug

See: http://false.ekta.is/2013/07/bash-tab-completion-for-python-scripts/
[timer-tests] Make all tests run

Can't figure out how to make contiki run a set of processes one by one, and
it's not the aim of my current project, so just run them all in a row inside
one big test process.
[timer-tests] Add test for clock_seconds()
[timer-tests] Add basic rtimer test