Fix creation of systemd service

[dmitry-g]

• Bump cookbook version to 0.3.0
• Lock systemd version to ~> 3.2.2
• Move description, after and condition_path_exists under unit section

This patch fixes the following issue:

05:34:25        NoMethodError
05:34:25        -------------
05:34:25        undefined method `description' for Custom resource systemd_service from cookbook systemd
05:34:25        
05:34:25        Relevant File Content:
05:34:25        ----------------------
05:34:25        /tmp/kitchen/cache/cookbooks/exabgp/recipes/default.rb:
05:34:25       
05:34:25         74:  systemd_service 'exabgp' do
05:34:25         75>>   description 'ExaBGP service'
05:34:25         76:    after node[:exabgp][:systemd][:after]
05:34:25         77:    condition_path_exists '/etc/exabgp/exabgp.conf'
05:34:25         78:  
05:34:25         79:    service do
05:34:25         80:      environment 'exabgp_daemon_daemonize' => 'false'
05:34:25         81:      exec_start '/usr/src/exabgp/sbin/exabgp /etc/exabgp/exabgp.conf'
05:34:25         82:      exec_reload '/bin/kill -s USR1 $MAINPID'
05:34:25         83:      user 'nobody'
05:34:25         84:    end

[ernestas-vinted]

maybe lock systemd version as well to prevent future failures