Implement Python standard library module tests

This commit adds:

* all optional dependencies of Python
* test that all standard library modules actually install and work
Fix petsc to build again on Linux
Python: make bzip2 and openssl deps optional

Only use them on linux. Update tests to include bzip2 and openssl explicitly.
Fix the test.host-scipy.yaml test

We need to specify the 'build_with' option to Python.
Remove 'python-readline' dep. from ipython

The readline module is now build into Python itself, so this extra module is
not necessary anymore.
added patch from homebrew to fix ncurses on clang
Merge pull request #56 from hashdist/python_mods2_branch

Implement Python standard library module tests