pywatchman: use binascii.hexlify in tests
pywatchman: use binascii.hexlify in tests

Python 3 no longer has `encode` on bytestrings.

kwlzn/watchman,wez/watchman,dhruvsinghal/watchman,nodakai/watchman,wez/watchman,nodakai/watchman,facebook/watchman,dhruvsinghal/watchman,dhruvsinghal/watchman,kwlzn/watchman,facebook/watchman,kwlzn/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,wez/watchman,dhruvsinghal/watchman,kwlzn/watchman,nodakai/watchman,wez/watchman,dhruvsinghal/watchman,dhruvsinghal/watchman,nodakai/watchman,facebook/watchman,dhruvsinghal/watchman,kwlzn/watchman,dhruvsinghal/watchman,wez/watchman,facebook/watchman,wez/watchman,wez/watchman,kwlzn/watchman,nodakai/watchman,facebook/watchman,wez/watchman,kwlzn/watchman,wez/watchman,facebook/watchman,nodakai/watchman