Minor refinements

Some minor refinements should be eventually made for collectagent and dcdbpusher to be consistent with each other:

• Option for defining cache interval is -c in dcdbpusher, -C in collectagent. It should be made uniform for both programs (-c in collectagent is used for the cassandra host);
• Make the syntax of configuration files uniform (e.g. True for boolean values is in some cases "on", in others "true" -> use only one value);
• Add logging to the collectagent using the BOOST facility like in dcdbpusher;
• Rename the global.conf configuration file for dcdbpusher to dcdbpusher.conf or pusher.conf;
• Add display of default values for command line options in dcdbpusher, like the collectagent does.