Handle database credentials better.

Rather than requiring the gulp-clobber.json file to contain username/password try and retrieve these from tnsnames.ora.
- user/password in gulp-clobber.json.
- Prompt user that nothing yet exists, get them to enter it at command line and write gulp-clobber.json file.

Is it possible to put usernames/passwords in tnsnames.ora and look them up from there?
