The description of xxx_LOG_FILE is not complete

Having `OCIS_LOG_FILE` respectively `xxx_LOG_FILE`, the description says:

`The path to the log file. Activates logging to this file if set.`

There is no default set - ok.

For completeness, we should write:
`The path to the log file. Activates logging to this file if set. Defaults to console output if unset.`

To be added in [all servcies](https://doc.owncloud.com/ocis/next/deployment/services/env-vars-special-scope.html#global-environment-variables).

@micbar @kobergj fyi