Fixes #5810: Implement a command to collect and send metrics

http://www.rudder-project.org/redmine/issues/5810

Replaces https://github.com/Normation/rudder-tools/pull/22
When I tested this, it didn't work because ldapsearch was not in the PATH. Our ldapsearch is available in /opt/rudder/bin, could you also look for it there?