stbt-run: Clearer error message on wait_for_match timeout
stbt-run: Clearer error message on wait_for_match timeout

A single run can have quite a lot of output, and the FAIL message was
hard to spot. Now it's at the very end of the output, which is the
first thing you look at, and is consistent with the normal backtrace
order.

Example output (before this change):

    stbt-run: Match 0 found at 0,0 (last: 696,578) with dimensions 10...
    stbt-run: Match 0 found at 0,0 (last: 0,0) with dimensions 105x32...
    stbt-run: Match 0 found at 0,0 (last: 0,0) with dimensions 105x32...
    stbt-run: Match 0 found at 0,0 (last: 0,0) with dimensions 105x32...
    stbt-run: Match 0 found at 0,0 (last: 0,0) with dimensions 105x32...
    FAIL: tests/test_manual_networking_setup/test.py: Didn't find match
        for 'tests/test_manual_networking_setup/Settings-label.png'
        after 10 seconds. Saved screenshot to 'screenshot.png'
      File "stb-tester/stbt-run", line 19, in <module>
        execfile(args.script)
      File "tests/test_manual_networking_setup/test.py", line 4, in <...
        wait_for_match('Settings-label.png')
      File "stb-tester/stbt.py", line 39, in wait_for_match
        return display.wait_for_match(*args, **keywords)
      File "stb-tester/stbt.py", line 202, in wait_for_match
        raise MatchTimeout(buf, template, timeout_secs)

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