registry._setup_database.lock remove issue when search_backend setting to sqlalchemy

[harrisonfeng]

Hi, All
I was experiencing the following issue when search_backend setting to sqlalchemy
cannot remove registry._setup_database.lock as it is not existing at all.
That's is to say, it try to remove this non-existing file.
I created a pull request here below, please review it.

Pull Request: #917 1009c49

Here is log:

OSError: [Errno 2] No such file or directory: './registry._setup_database.lock'
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 507, in spawn_worker
    worker.init_process()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/workers/ggevent.py", line 193, in init_process
    super(GeventWorker, self).init_process()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/workers/base.py", line 114, in init_process
    self.wsgi = self.app.wsgi()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/base.py", line 66, in wsgi
    self.callable = self.load()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/wsgiapp.py", line 65, in load
    return self.load_wsgiapp()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/wsgiapp.py", line 52, in load_wsgiapp
    return util.import_app(self.app_uri)
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/util.py", line 356, in import_app
    __import__(module)
  File "/usr/local/lib/python2.7/dist-packages/docker_registry/wsgi.py", line 28, in <module>
    from .search import *  # noqa
  File "/usr/local/lib/python2.7/dist-packages/docker_registry/search.py", line 14, in <module>
    INDEX = index.load(cfg.search_backend.lower())
  File "/usr/local/lib/python2.7/dist-packages/docker_registry/lib/index/__init__.py", line 82, in load
    return db.SQLAlchemyIndex()
  File "/usr/local/lib/python2.7/dist-packages/docker_registry/lib/index/db.py", line 86, in __init__
    self._setup_database()
  File "/usr/local/lib/python2.7/dist-packages/docker_registry/toolkit.py", line 353, in wrapper
    os.remove(lock_path)
OSError: [Errno 2] No such file or directory: './registry._setup_database.lock'
[2015-01-29 08:21:40 +0000] [17] [INFO] Worker exiting (pid: 17)
[2015-01-29 08:21:40 +0000] [15] [INFO] Worker exiting (pid: 15)
Traceback (most recent call last):
  File "/usr/local/bin/gunicorn", line 11, in <module>
    sys.exit(run())
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/wsgiapp.py", line 74, in run
    WSGIApplication("%(prog)s [OPTIONS] [APP_MODULE]").run()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/base.py", line 185, in run
    super(Application, self).run()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/base.py", line 71, in run
    Arbiter(self).run()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 196, in run
    self.halt(reason=inst.reason, exit_status=inst.exit_status)
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 292, in halt
    self.stop()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 343, in stop
    time.sleep(0.1)
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 209, in handle_chld
    self.reap_workers()
  File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 459, in reap_workers
    raise HaltServer(reason, self.WORKER_BOOT_ERROR)
gunicorn.errors.HaltServer: <HaltServer 'Worker failed to boot.' 3>
lxc-start: The container failed to start.
lxc-start: Additional information can be obtained by setting the --logfile and --logpriority options.