Rex::Commands::Inventory throws warnings if netstat not installed

[djzort]

As below

[2017-10-11 21:51:29] ERROR - Error executing task:
[2017-10-11 21:51:29] ERROR - Error running netstat at /home/dean/perl5/perlbrew/perls/perl-5.20.2/lib/site_perl/5.20.2/Rex/Hardware/Network/Linux.pm line 225.

[2017-10-11 21:51:29] ERROR - 1 out of 2 task(s) failed:
[2017-10-11 21:51:29] ERROR - 	fix_hosts_file failed on nextcloud01
[2017-10-11 21:51:29] ERROR - 		Error running netstat at /home/dean/perl5/perlbrew/perls/perl-5.20.2/lib/site_perl/5.20.2/Rex/Hardware/Network/Linux.pm line 225.

Probably it should handle netstat's absence nicely