profile.py: stop exposing private methods of TestProfile

This patch stops exposing flatten_group_hierarchy and prepare_test_list
by marking them with a leading underscore. These methods weren't meant
to be called outside, and this is the pythonic way of letting users know
that these are "private" methods.
profile.py: set __all__

Setting the __all__ name in a module controls which names it exposes
when imported.
framework: rename profile.loadTestProfile to profile.load_test_profile

This is a more pythonic name for this method.

This patch was created with the following shell command:
find . -name '*py' | \
xargs sed -i -e 's!loadTestProfile!load_test_profile!g'