Wait for graph DB on startup

[bzurkowski]

12:48:39 probe.1 | During handling of the above exception, another exception occurred:
12:48:39 probe.1 |
12:48:39 probe.1 | Traceback (most recent call last):
12:48:39 probe.1 |   File "/usr/local/bin/orca-probe", line 8, in <module>
12:48:39 probe.1 |     sys.exit(main())
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/orca/cmd/probe.py", line 20, in main
12:48:39 probe.1 |     probe_manager.initialize()
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/orca/topology/manager.py", line 37, in initialize
12:48:39 probe.1 |     graph.Graph.get(graph_lock).setup()
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/orca/graph/graph.py", line 87, in setup
12:48:39 probe.1 |     self._driver.setup()
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/orca/graph/drivers/arangodb.py", line 67, in setup
12:48:39 probe.1 |     if not sys_db.has_database(self._database_name):
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/database.py", line 729, in has_database
12:48:39 probe.1 |     return name in self.databases()
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/database.py", line 719, in databases
12:48:39 probe.1 |     return self._execute(request, response_handler)
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/api.py", line 66, in _execute
12:48:39 probe.1 |     return self._executor.execute(request, response_handler)
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/executor.py", line 81, in execute
12:48:39 probe.1 |     resp = self._conn.send_request(request)
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/connection.py", line 161, in send_request
12:48:39 probe.1 |     auth=self._auth
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/arango/http.py", line 109, in send_request
12:48:39 probe.1 |     auth=auth
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/requests/sessions.py", line 530, in request
12:48:39 probe.1 |     resp = self.send(prep, **send_kwargs)
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/requests/sessions.py", line 643, in send
12:48:39 probe.1 |     r = adapter.send(request, **kwargs)
12:48:39 probe.1 |   File "/usr/local/lib/python3.7/site-packages/requests/adapters.py", line 516, in send
12:48:39 probe.1 |     raise ConnectionError(e, request=request)
12:48:39 probe.1 | requests.exceptions.ConnectionError: HTTPConnectionPool(host='arangodb', port=8529): Max retries exceeded with url: /_db/_system/_api/database (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f6da2c2f8d0>: Failed to establish a new connection: [Errno 111] Connection refused'))