A sudo-enabled ubuntu user may now use system ruby

Prior to this commit, ubuntu users had to use rbenv.  Now, as was
already the case with rhel6/fc16/fc17, a sudo-enabled user may instead
use system ruby.
Merge pull request #19 from cwolferh/ubuntu_sysruby

A sudo-enabled ubuntu user may now use system ruby
Allow checking out of any project tags or commit hashes

Prior to this commit, could only checkout branches by name.  Now, env
variables such as export FACTER_CONDUCTOR_BRANCH may specify a branch,
tag or commit hash.
Merge pull request #21 from cwolferh/allow_git_checkout_tags

Allow checking out of any project tags or commit hashes
Merge remote branch 'upstream/master' into aeolus-image-rubygem-versionfix