Issue #131 solution: remove test output directories. This is rebased on fix_gauge_path branch (issue # 224)

I set claw.output_format = None for all the tests so that the output is not written in an outdir, Except for the psystem test where I'm testing gauges (and I'll add some code for the gauges IO later), I added a code to cleanup this test outputs.

Note that this pull request depends on the issue #224 (pull request for test gauge pathes).
because before this fix for gauge pathes, gauges will be always written to _outdir/_gauges
no matter what claw.outdir was.