ncm-cups 17.7.0: configuration of ServerAlias + miscellanous enhancements

[jouvin]

In 17.7.0, ncm-cups allows only to configure the ServerName attribute. It would be good to allow to configure the ServerAlias too. This configuration module also deserves some cleanups and enhancements. The main tasks required are:

• ServerAlias configuration support
• Removal of code to support legacy schema (not allowed by the current schema)
• Promote warnings raised in case of printer configuration errors to errors: this will allow the printer configuration to be retried at the next profile deployment, in the case of a transient problem (as it happens sometimes at boot time when cupsd is started but no yet answering requests)
• Check existence of the printer PPD file if explicitly defined
• Additon of unit tests for the main features
• Use CAF Rule-Based Editor to replace the config parser embedded in the config module (originally derived from ncm-dpmlfc, the ancestor of CAF RBE)