Entrypoint issues when using custom DEDICATED_CFG

[KemTM]

Based on what I see on the entrypoint.sh file there are a couple of problems that I encountered when using my own supplied config and setting DEDICATED_CFG env.

1. Despite the dedicated server authorization infos (masterserver login+password) entered in my config file, the entrypoint still demands that MASTER_LOGIN and MASTER_PASSWORD envs are set. This can be worked around by supplying dummy values.
2. Despite using a different config file, the entrypoint still writes the defaults (and the aforementioned masterserver account dummies) to dedicated_cfg.txt, which is not necessary and can even be harmful if UserData volume is shared across multiple containers.