Handle incorrect DB credentials better.

The following discussion from !87 (merged) should be addressed:

@tomek started a discussion: (+1 comment)
Install server using DEB on ubuntu 19.10. I did not modify server.env yet. Here's what I saw:
```
mar 13 12:34:10 billabong stork-server[13274]: INFO[2020-03-13 12:34:10]             main.go:18    Starting Stork Server, version 0.4.0, build date 2020-03-13 10:13
mar 13 12:34:10 billabong stork-server[13274]: database password:
mar 13 12:34:10 billabong stork-server[13274]: 2020/03/13 12:34:10 inappropriate ioctl for device
```
Two comments:
1. printing database password must go away.
2. the "inappropriate ioctl for device" message is confusing. I suspect the reason is that I haven't set values in server.env, but the error message should be more meaningful. Maybe some check if those are not defined or empty? Some empty params are ok (e.g. password).