Bootstrap scripts now use '#!/usr/bin/env python' instead of
'#!/usr/bin/env python3' which should let them work on a wider variety
of systems. Tested again with python 2 and made a couple minor changes
for compatibility.
Added check_auth() function to update.py. If it fails, it prints a
useful error message and gets ABORT_PW_ENVSETUP=1 added to the
environment. This is a cue to env_setup/setup.sh to not continue so the
error is prominent on the terminal. (env_setup/setup.sh clears this
variable so it won't persist into the next time env_setup/setup.sh is
sourced.)
Change-Id: Ib4a694178f1dce8971302914651feea3c727ea15
