WIP: adding chef exec
remove unused ruby_engine
use exec instead of mixlib-shellout
refactor omnibus path stuff
add Gem.default_bindir to PATH

this is still /opt/chef/embedded/bin not the user's homedir tho
fix the verify command
fix user bin dir
correct user_bin_dir
fix verify specs
add basic specs for exec command
add a chef exec rspec test for the failure case
replace envvar 'cheat' with proper Gem method
replace envvar 'cheat' with proper Gem method
add omnibus_env helper
Merge pull request #22 from opscode/lcg/chef-exec

add chef exec command