fixes #63 client conf override issue

- Using the value from `rsyslog::client_conf` to set the file name for `/etc/rsyslog.conf/<client_file>.conf` in the module `rsyslog::client`. _This defaults to the value in `rsyslog::params::client_conf` or `/etc/rsyslog.conf/client.conf`._
- Using the value from `rsyslog::server_conf` to set the file name for `/etc/rsyslog.conf/<server_file>.conf` in the module `rsyslog::server`. _This defaults to the value in `rsyslog::params::server_conf` or `/etc/rsyslog.conf/server.conf`._

Maintained functionality from before the edit if the variables are not set. The default value in rsyslog::params for client_conf and server_conf needed to be modified in order to not modify the file name in `rsyslog::snippet`. However, the client_conf and server_conf variables from `rsyslog::params` were unused.