test.rb: Add python to PATH in test env
test.rb: Add python to PATH in test env

Python is now a regular dependency, looking
for it in the requirements does not work anymore.

Closes Linuxbrew/brew#593.

Signed-off-by: Michka Popoff <7b0496f66f66ee22a38826c310c38b415671b832@gmail.com>

hanxue/linuxbrew,maxim-belkin/brew,Linuxbrew/brew,Linuxbrew/brew,Linuxbrew/brew,Linuxbrew/brew,hanxue/linuxbrew,maxim-belkin/brew,maxim-belkin/brew,hanxue/linuxbrew