Use "cups-config --serverbin" to detect the presence of cupsddk

[Daniel Pielmeier]

In installer/core_install.py the presence of cupsddk is checked by searching for the file drv under /usr/lib/cups/driver. However if the path is different because the "serverbin" path is configured otherwise the cupsddk check fails although it is working properly. The attached patch makes use of cups-config to determine the correct path.

[Daniel Pielmeier (daniel-pielmeier)]

Now that cupsddk is obsolete, I think this bug can be closed now.