Basic acceptance test with beaker

Just includes the class and check collectd package present and service running
Fix Puppet deprecation warning

Example:

```
Warning: Variable access via 'port' is deprecated. Use '@port' instead. template[/etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb]:6
   (at /etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb:6:in `result')
Warning: Variable access via 'timerpercentile' is deprecated. Use '@timerpercentile' instead. template[/etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb]:21
   (at /etc/puppet/modules/collectd/templates/plugin/statsd.conf.erb:21:in `result')
```
Fix travis by using plabs gemfile
Add cpufreq plugin doc
Add cpufreq plugin
curl: fix handling of some parameters

 - $verifypeer/$verifyhost/$measureresponsetime: properly handle undef vs. false
 - $matches: default value (array with empty hash) creates bad config (match
   block with missing values)
 - $matches: match blocks are optional if measureresponsetime is enabled
Add conntrack module
Uses the LoadPlugin syntax with bracket when supported

This is fully backwards compatible.

The version check is done exactly how it's supposed to ; I checked the
sources of collectd to be sure there's no conflict.

Globals has always defaulted to false so I'm making it default to false
in this module. I'm not setting it undef because that's a boolean and we
got issues with checking if a boolean is false or undef (see #182).
Cleaning the now redundant LoadPlugin declaration
Add rspec test to ensure the bracket syntax is using when available
Basic acceptance test with beaker

Just includes the class and check collectd package present and service running