Use /usr/bin/env, not /bin/env

/usr/bin/env is more portable (/bin/env does not exist on SUSE).
Also address minor nit on review about python 3.x compatibility.

Change-Id: I6bc1a579bb43664f4d2be35a96f45189a6df0e27
Merge "Use /usr/bin/env, not /bin/env"