use a system-independent shebang line in rebuild-iptables script

[WattsInABox]

Fixes #18

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[juliandunn]

So... it's not quite that easy, because Ruby isn't necessarily in the path on systems that don't otherwise have Ruby but only have the Chef Client full-stack-installer package there. That's why there's this "complication".

For example, I have a Fedora system which only has the RPM. Invoking /usr/bin/env ruby on this box doesn't find Ruby, and the binstubs for Chef itself in /usr/bin/chef-{apply,client,solo,shell} have a hardcoded hashbang to /opt/chef/embedded/bin/ruby for this purpose.

[WattsInABox]

Well that's weird cause the iptable stuff didn't work on our centos systems until I made this change...

[WattsInABox]

Thanks for the education on the system-independence issue, though. So how else can we fix it? Make the code a little more complicated to try and find the right ruby?

I can also try that hardcoded hashbang line to see if it works now. Maybe I was doing something else wrong.

[juliandunn]

I kind of feel like the current behavior is adequate; either that, or just substitute the second term in the ternary expression to /usr/bin/env ruby.

[tas50]

At it stands this breaks chef users that don't have a system ruby installed. I think something could be put together to check to see if /usr/bin/env ruby returns true and if not use chef's ruby, but I'm going to close this PR out for now.

[WattsInABox]

so maybe changing this

variables(      
   :hashbang => ::File.exist?('/usr/bin/ruby') ? '/usr/bin/ruby' : '/opt/chef/embedded/bin/ruby'        
)

to something like this

def system_ruby
  '/usr/bin/env ruby'
end

def system_ruby_installed?
  `#{system_ruby} --help` != ''
end

variables(    
   :hashbang => system_ruby_installed? ? system_ruby : '/opt/chef/embedded/bin/ruby'    
)

?