unix_machine files_different? fails on solaris

[steversmith]

Summary:

When using a solaris based box, I get the following error:

RuntimeError: Error: command 'md5 -r /etc/chef/client.rb' exited with code 1

This is traced to the unix_machine.rb files_different? method, which attempts to use md5sum -b #{path}, followed by md5 -r #{path}, if the md5sum command fails.

Suggested fix:

A fix for solaris is to include using digest -a md5 #{path} if both md5sum and md5 commands fail.