Make the script that checks for undefined Android symbols compatible
with both Python 2 and Python 3, to allow for future updates to the
default system Python on our build machines.
I'd like to land this before https://github.com/servo/saltfs/pull/249.
We currently use Ubuntu 14.04 (an LTS release); Ubuntu is aiming for
Python 3 as the default Python in the next LTS release, 16.04, and
I'd like to have any scripts be ready for the transition.