adds defaultText for all options that use `cfg.*` values in their
defaults, but only for interpolations with no extra processing (other
than toString where necessary)
Without `ROOT_PATH` set, `gogs serv` tries to open logs in writing in
its store directory. This blocks cloning or pushing over ssh, and
results in a gogs internal error.
If neither database.password or database.passwordFile were provided,
it would try and fail to coerce null to a string.
This fixes the situation where there is no password for the database.
Resolves#27950
Pushing to gogs only works if the `gogs` user's shell is `bash`. For error and
solution, refer to [this SO thread](http://stackoverflow.com/a/22315659)
