Import interrupted by rollout breaks because of lock contention

  affects launchpad-code

The evolution import from git was just about to finish when a new
version of Launchpad was rolled out. This seems to've killed an active
bzr process and has left the lock open:

Traceback (most recent call last):
  File "/srv/importd.launchpad.net/production/launchpad-rev-8939/scripts/code-import-worker.py", line 66, in <module>
    script.main()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8939/scripts/code-import-worker.py", line 61, in main
    import_worker.run()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8939/lib/lp/codehosting/codeimport/worker.py", line 393, in run
    self._doImport()
  File "/srv/importd.launchpad.net/production/launchpad-rev-8939/lib/lp/codehosting/codeimport/worker.py", line 491, in _doImport
    self.source_details.branch_id, bazaar_tree, self.required_format)
  File "/srv/importd.launchpad.net/production/launchpad-rev-8939/lib/lp/codehosting/codeimport/worker.py", line 89, in push
    branch_to.pull(branch_from, overwrite=True)
  File "<string>", line 2, in pull_write_locked
  File "/home/pqm/for_rollouts/production/eggs/bzr-2.1.0b4-py2.5-linux-x86_64.egg/bzrlib/branch.py", line 2151, in lock_write
  File "/home/pqm/for_rollouts/production/eggs/bzr-2.1.0b4-py2.5-linux-x86_64.egg/bzrlib/lockable_files.py", line 193, in lock_write
  File "/home/pqm/for_rollouts/production/eggs/bzr-2.1.0b4-py2.5-linux-x86_64.egg/bzrlib/lockdir.py", line 583, in lock_write
  File "/home/pqm/for_rollouts/production/eggs/bzr-2.1.0b4-py2.5-linux-x86_64.egg/bzrlib/lockdir.py", line 551, in wait_lock
bzrlib.errors.LockContention: Could not acquire lock "LockDir(sftp://hoover@escudero/srv/importd/www/0004b37f/.bzr/branch/lock)":
Import failed:
Traceback (most recent call last):
Failure: twisted.internet.error.ProcessTerminated: A process has ended with a probable error condition: process ended with exit code 1.