Update omnibus to pull in updated `ffi-yajl` and `libyajl2`
Merge pull request #197 from opscode/schisamo/install-fix

Update omnibus to pull in updated `ffi-yajl` and `libyajl2`
Output a SemVer compliant build version string

We currently use the `:git_describe` version for all chef-client 
projects. This build version format does not respect 
`Omnibus::Config.append_timestamp` which in turn causes two different 
builds to produce packages named identically. This can wreck havoc on 
when packages are published to backends like Omnitruck and Artifactory.
[WIP] Override the chef version for testing