run_tests.sh should return failure on pep8 failure

run_tests.sh on r47:

bin/glance-upload:44:13: E225 missing whitespace around operator
    print >>sys.stderr, msg
            ^
    - Always surround these binary operators with a single space on
      either side: assignment (=), augmented assignment (+=, -= etc.),
      comparisons (==, <, >, !=, <>, <=, >=, in, not in, is, is not),
      Booleans (and, or, not).

    - Use spaces around arithmetic operators.

    Okay: i = i + 1
    Okay: submitted += 1
    Okay: x = x * 2 - 1
    Okay: hypot2 = x * x + y * y
    Okay: c = (a + b) * (a - b)
    Okay: foo(bar, key='word', *args, **kwargs)
    Okay: baz(**kwargs)
    Okay: negative = -1
    Okay: spam(-1)
    Okay: alpha[:-i]
    Okay: if not -5 < x < +5:\n pass
    Okay: lambda *args, **kw: (args, kw)

    E225: i=i+1
    E225: submitted +=1
    E225: x = x*2 - 1
    E225: hypot2 = x*x + y*y
    E225: c = (a+b) * (a-b)
    E225: c = alpha -4
    E225: z = x **y

run_tests.sh should be failing (and therefore holding up Hudson merging) when pep8 fails.