stbt-debug directory removed if test which creates it passes
stbt-debug directory removed if test which creates it passes

test_detect_motion_with_debug_output_does_not_segfault_without_mask
creates the stbt-debug directory as part of the test but previously did
not clean it up on completion.

martynjarvis/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,wmanley/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester