Health Check Fixes

This PR works to lock down a number of software definitions that were previously linking against system libraries vs the embedded libs generated by an Omnibus project. 

The issues were uncovered when we began installing git 1.9.0 from source on our build slaves. Compiling git requires a [number of development libraries](https://github.com/opscode-cookbooks/omnibus/blob/master/recipes/_git.rb#L32-L56) of which our Omnibus builds began linking against.

Highlights include:

* Curl should ignore `gnutls` and `librtmp`
* Skip building Perl extensions that are known to link against system libs.
* Ensure `nokogiri` links against embedded zlib.
* Bump `nokogiri`'s default_version to 1.6.1.
* Bump `curl` to 7.36.0 - contains fixes for recent security vulnerabilities

/cc @opscode/release-engineers @opscode/engineering-leads @opscode/client-eng