Output a SemVer compliant build version string in all Client projects

We currently use the `:git_describe` version for all 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.

I've had conversations with @sersut about why we are clinging to the `:git_describe` version in client projects and it's related to Chef bootstrapping (`knife bootstrap`). The bootstrapping process pulls the Chef version from the internal Chef gem. This version string is in turn sent in the request to Omnitruck. Rubygem's handles pre-release version numbers slightly different than SemVer does. In particular it separates the `MAJOR.MINOR.PATCH` from the pre-release indicator with a dot (`.`) instead of a dash (`-`) (e.g. `11.14.0.rc.2` vs `11.14.0-rc.2`).

I've done some testing and Omnitruck does in fact "do the right thing". It treats Rubygem and Semver pre-release versions identically and properly retrieves metadata and packages. This works because Omnitruck now [parses any version string into an `Opscode::Version` instance](https://github.com/opscode/opscode-omnitruck/blob/rel-1.1.11/app.rb#L224-L270) before doing comparisons or queries.

Here are examples of requesting metadata for Chef 11.14.0.rc.2 in Rubygem and SemVer formatted version strings:

```
$  curl "http://www.getchef.com/chef/metadata?p=ubuntu&pv=12.04&m=x86_64&v=11.14.0.rc.2&prerelease=true"
url	http://opscode-omnibus-packages.s3.amazonaws.com/ubuntu/12.04/x86_64/chef_11.14.0.rc.2-1_amd64.deb
md5	716f8bffec19e7dddfc9ea0b8813953f
sha256	7b9c80ac3e2fcf00a7335da2ad003c991cf6e67d0b9b94f11b160bb0682d231c
$  curl "http://www.getchef.com/chef/metadata?p=ubuntu&pv=12.04&m=x86_64&v=11.14.0-rc.2&prerelease=true"
url	http://opscode-omnibus-packages.s3.amazonaws.com/ubuntu/12.04/x86_64/chef_11.14.0.rc.2-1_amd64.deb
md5	716f8bffec19e7dddfc9ea0b8813953f
sha256	7b9c80ac3e2fcf00a7335da2ad003c991cf6e67d0b9b94f11b160bb0682d231c
```

So in conclusion (sorry for the essay) we can safely move all Client projects to SemVer build versions!

/cc @opscode/release-engineers @opscode/client-engineers @christophermaier 
@sersut This change (and the one you comment on below) are part of a `[WIP]` commit. This basically means the commit will be removed before merging.