Modify server so that startup is not dependent on a running database

[njriasan]

For our usercloud architecture design we want to have the mongodb container mount an encrypted filesystem directly. However the server needs to give mongo the key at launch, so we need the server already running and not dependent on mongo.

[shankari]

It seems like the obvious solution for this (at least with the current e-mission-server code) is to lazily initialize the connection to the database.

[shankari]

@njriasan fix is at e-mission/e-mission-server#675
I am OK with merging one part (assuming it passes tests).
You need to apply a manual patch for the second part (e-mission/e-mission-server#675 (comment))

Please see the testing done for more details.