[cpt.py] --check-requirements doesn't detect Homebrew as a package manager and misdetect libz (zlib) dependecy

Another interesting issue, I noticed about cpt.py that on macOS it looks like it requires Macports for an (optional?) Zlib dependency:
https://gist.github.com/oshadura/26ae5b7b07c37bfd2b19aa2671858147 

I have homebrew and definitely I have libz here: /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk/usr/lib/libz.tbd (found version "1.2.11").

