Added collectd config to control plugins and transmit stats

the flags on the collectd class ensure that you get the plugins
you specify not the ones in the default conf file.

This then allows the specification of a plugin to send data to
to carbon on the graphite server, log to syslog and to collect
baseline stats.
puppet script tidy up and additional comments
Merge pull request #4 from gds-operations/collectd_config

Collectd config