Allow including files based on hostname

[Marcel Baur]

Currently, it is possible to include configuration files with

 include /etc/monit/conf.d/*

For multi-server environemnts, it would be awesome to include configuration files based on $HOST, i.e.

 include /etc/monit/conf.d/$HOST.monitrc

This way, all hosts could share the same basic .monitrc with per-host exceptions in $HOST.monitrc