Wheel support in pip needs current setuptools

When virtualenvs are used without distribute and an old setuptools
python package is installed in the system, upgrading pip in the
virtualenv won't ensure setuptools > 0.8 is installed which is required
by the pip wheel command. This patch upgrades setuptools if distribute
isn't used.

Signed-off-by: Franz Pletz <fpletz@fnordicwalking.de>