Misleading error message on migrate number conflict when running unit tests

If two files in the nova/db/sqlalchemy/migrate_repo/versions directory have the same number, then run_tests.sh will not produce any output, and the run_tests.log file will have a misleading error message.

To reproduce:

$ touch nova/db/sqlalchemy/migrate_repo/versions/23_foo.py
$ ./run_tests.sh

No output will appear on standard out, and run_tests.log will contain the following:

2011-06-17 09:56:04,385 CRITICAL nova [-] 'NovaTestResult' object has no attribute 'start_time'
(nova): TRACE: Traceback (most recent call last):
(nova): TRACE: File "run_tests.py", line 358, in <module>
(nova): TRACE: sys.exit(not core.run(config=c, testRunner=runner, argv=argv))
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/core.py", line 283, in run
(nova): TRACE: return TestProgram(*arg, **kw).success
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/core.py", line 118, in __init__
(nova): TRACE: **extra_args)
(nova): TRACE: File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/unittest.py", line 817, in __init__
(nova): TRACE: self.runTests()
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/core.py", line 197, in runTests
(nova): TRACE: result = self.testRunner.run(self.test)
(nova): TRACE: File "run_tests.py", line 327, in run
(nova): TRACE: result_ = core.TextTestRunner.run(self, test)
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/core.py", line 61, in run
(nova): TRACE: test(result)
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/suite.py", line 176, in __call__
(nova): TRACE: return self.run(*arg, **kw)
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/suite.py", line 213, in run
(nova): TRACE: result.addError(self, self._exc_info())
(nova): TRACE: File "/Users/lorin/nova/trunk/.nova-venv/lib/python2.6/site-packages/nose/proxy.py", line 125, in addError
(nova): TRACE: self.result.addError(self.test, err)
(nova): TRACE: File "run_tests.py", line 258, in addError
(nova): TRACE: self._handleElapsedTime(test)
(nova): TRACE: File "run_tests.py", line 218, in _handleElapsedTime
(nova): TRACE: self.elapsed_time = time.time() - self.start_time
(nova): TRACE: AttributeError: 'NovaTestResult' object has no attribute 'start_time'

(This is revision 1188).