Merge pull request #10 from iggy/master

Fix ping plugin for unset host_from_grains in pillar
Merge pull request #11 from iggy/master

Add nginx plugin
adds map entry for RedHat based OS
Merge pull request #13 from sinnerschrader/feature/redhat_support

adds map entry for RedHat based OS
Add require on liboping package

For some reason, the service is getting restarted before the package is
installed (but after the config file is in place). So collectd tries and fails
to enable the ping plugin (without having the lib in place already).