Really fix OSX nightlies

Really fix OSX nightlies

After #3311 we're now correctly trying to link OpenSSL statically on
OSX. Unfortunately though this is failing to complete on the builders.
Turns out the way we install OpenSSL through Homebrew create "universal
archives" which is essentially an archive with both i686 and x86_64
object files, but separated. The linker takes care of this just fine but
rustc currently chokes on it, unable to include the library statically
into the compiler.

To work around this we prepare our own mini install of OpenSSL by
copying relevant bits into a local directory (like we do on Linux). As
part of this we use the `lipo` tool, which is used to manage these fat
archives, to disassemble the archive and only extract the relevant
architecture. This should make a pre-installation step which both
extracts the information and configures Cargo to use it.

This should also fix the errors we're seeing on Travis I believe.