Refactor states into smaller units

This patch splits the following into smaller units:

 * nagios.nrpe into .server and .plugin
 * nagios.server state into .server and .plugin

It also uses only a single map to keep all settings and create users and
groups in nagios.users
New config file handling for Arch and Debian

This is a commit that will break previous configurations as it unconditionally
changes the way in which configuration files are handled. In particular it
allows the user to configure nrpe.server with:

    - nrpe.cfg
    - nfpe_local.cfg
    - nrpe.d/*.cfg

which changes the previous way in which the recipe allowed to set the include
directory via pillars.

It is also changes the pillar structure and users will have to ensure that
they change their settings. In particular "nrpe:nagios_server" has been
renamed to "nrpe:server_address" and "include_dir" has been removed.

The following settings have been introduced:

    * server_port
    * allowed_hosts
    * command_timeout
    * connection_timeout
    * checks (list of checks to enable)
Do no install nrpe-plugin Recommends on Debian