-workdir Option Fix

The -workdir option specifys a directory for glastopf-runner, but Glastopf looked for the log/ directory and the glastopf.cfg file in the pwd. With this branch, glastopf looks for log/ and glastopf.cfg in the directory specified by -workdir. I made this fix so I could start glastopf-runner in an init script on boot without having to worry about the pwd for the script. This fix will make starting glastopf easier and cleaner.