Prepare for Python3, use print function

Use 2to3 to fixup all print statements to use the print function.

Update 'autofix/fiximports' to ensure that print_function is imported
from future.

Test Plan:

General coverage
$ ./precommit.sh
thread-subprocess-test: fix license notice
phab-ping: refactor for PyChecker

Refactor a complicated print statement by splitting it out a variable.

Test Plan:
$ ./precommit.sh
$ phab-ping http://127.0.0.1