Create LWRPs for plugins, includes and excludes (WIP)

including exclude_regex .

I'm a bit stuck because burp doesn't accept "config directories" (conf.d)
as expected.

This may have to be converted into hashes, populated at compile time.
Replace some LWRPs with definitions

The definitions run a ruby_block at compile_time to make sure that
the template[/etc/burp/burp.conf] will have an up-to date includes/excludes list
at the converge phase.

To use in a recipe:
burp_include '/var/lib/mysoft'
burp_exclude '/var/excludeme'
burp_exclude_regex '^myregex.*'

those definitions should be used instead of the corresponding node['burp']
attributes to avoid weird isssues because of the order of elements in the
run_list.

I'm trashing the idea of multiple clients on a node for now.
(the burp_client LWRP)

*The lazy block in providers/client.rb requires Chef >= 11.6*
Search for clients in the server recipe

partial_search() requires:
- Chef Server >= 11.0.4
- Chef Client >= 11.10.0 or the partial_search cookbook

It's faster than pulling the entire nodes' data with search().
(forgot to add server attributes)
Create /run/burp/ only via Upstart
Fix server's notify_script location
Fix server's 'timer_arg's
Create 'burp' upstart & cron jobs for initiating a backup

- Try to run at 17h00
- - Sleep 0-30 seconds
    (NTP-synced servers will stampede otherwise)
- sleep 5 minutes between tries
- stop trying at 6h00