fix hostname plugin + add machinename variable

- removes :sigar platform that isn't a platform
- aix and hpux fall back to sigar/default behavior
- adds machinename attribute for raw output of 'hostname' command
  with no DNS trickery
add :aix and :hpux back in as targets again

- :default would cover it, but this makes it explicit
remove shitty solaris logic

- it assumes hostname is short and it may not be (e.g. smartos)
- it uses the NIS domainname as the DNS domainname which is both
  unlikely to be used these days and not guaranteed to match anyway
- its unlikely this worked correctly for just about anyone
- in the event that the domainanme was blank you got a trailing dot
  which screwed everything up.
normalize fqdn across the platforms

- platforms that didn't have hostname -f now get the same behavior
  for node['fqdn'] as linux via pure ruby
add sigar_is_available? check
Merge pull request #265 from opscode/lcg/fix-hostname-plugin

fix hostname plugin + add machinename variable