Ensure bridge script tests use Python 2 and Python 3
Ensure bridge script tests use Python 2 and Python 3

Explicitly look for /usr/bin/python2 and /usr/bin/python3 and ensure
unit tests are executed with each version of Python found on the testing
system. If no version of Python is found then the TestSetupSuite will
fail, failing all the tests.

bz2/juju,frankban/juju,marcmolla/juju,dimitern/juju,bogdanteleaga/juju,mjs/juju,alesstimec/juju,dooferlad/juju,AdamIsrael/juju,macgreagoir/juju,gabriel-samfira/juju,waigani/juju,dooferlad/juju,waigani/juju,gabriel-samfira/juju,mikemccracken/juju,waigani/juju,makyo/juju,AdamIsrael/juju,marcmolla/juju,waigani/juju,mjs/juju,anastasiamac/juju,howbazaar/juju,mjs/juju,perrito666/juju,kat-co/juju,dimitern/juju,alesstimec/juju,mikemccracken/juju,frankban/juju,axw/juju,bz2/juju,makyo/juju,dimitern/juju,ericsnowcurrently/juju,anastasiamac/juju,bz2/juju,axw/juju,marcmolla/juju,perrito666/juju,anastasiamac/juju,macgreagoir/juju,howbazaar/juju,macgreagoir/juju,dooferlad/juju,dimitern/juju,dimitern/juju,bogdanteleaga/juju,kat-co/juju,mjs/juju,ericsnowcurrently/juju,kat-co/juju,marcmolla/juju,axw/juju,mjs/juju,reedobrien/juju,mikemccracken/juju,makyo/juju,gabriel-samfira/juju,alesstimec/juju,frankban/juju,perrito666/juju,howbazaar/juju,bac/juju,mjs/juju,bac/juju,kat-co/juju,alesstimec/juju,macgreagoir/juju,axw/juju,reedobrien/juju,alesstimec/juju,mjs/juju,bac/juju,ericsnowcurrently/juju,ericsnowcurrently/juju,axw/juju,reedobrien/juju,ericsnowcurrently/juju,howbazaar/juju,dooferlad/juju,bz2/juju,anastasiamac/juju,mikemccracken/juju,bz2/juju,marcmolla/juju,macgreagoir/juju,dooferlad/juju,makyo/juju,gabriel-samfira/juju,gabriel-samfira/juju,howbazaar/juju,AdamIsrael/juju,perrito666/juju,frankban/juju,bac/juju,kat-co/juju,reedobrien/juju,AdamIsrael/juju,anastasiamac/juju,perrito666/juju,bogdanteleaga/juju,bogdanteleaga/juju,frankban/juju,reedobrien/juju,bac/juju,mikemccracken/juju