Added `MONGODB_USER`, `MONGODB_PASSWORD` and `MONGODB_DATABASE` parameters to
create user and database at first run.
The `MONGODB_USER` (default: `root`) and `MONGODB_PASSWORD` parameters
indicate if authentication `--auth` is enabled on the server,
else the server allows unauthenticated access.
The user is created only if `MONGODB_PASSWORD` is also specified. The
default `root` user is assigned `userAdminAnyDatabase` role on the
`admin` database giving the `root` user complete administrative
access to the mongo server.
Sameer Naik