Setting `MONKEY_MONGO_URL` env variable to non-default value results in island exiting with error

Describe the bug

The mongo URL is configurable via the MONKEY_MONGO_URL environment variable. However, Flask-Security also has a connection to mongodb, and it uses hard-coded values instead of the connection details from MONKEY_MONGO_URL. Thus, if MONKEY_MONGO_URL differs from the defaults, the server will error out because one of the connections to mongo will fail.

Introduced in 564c15dc1cc2395151a545ea89f1d9ff9260becc #2157

To Reproduce

Steps to reproduce the behavior:

1. Setup and run mongodb on a different port (e.g. 27019)
2. Set MONKEY_MONGO_URL environment variable with the port (e.g. mongodb://localhost:27019/monkey_island)
3. Run the island
4. Observe that the island exits because it failed to connect to mongodb

Expected behavior

I expect both connections to mongodb to use the same connection details.

Machine version (please complete the following information):

• OS: Windows or Linux