pywatchman: normalize root paths for subscription data
pywatchman: normalize root paths for subscription data

Summary: Without this, using the client can be non-deterministic, particularly on Windows, but potentially also on mac.

Reviewed By: sid0

Differential Revision: D4332147

fbshipit-source-id: 3a9c11e81e24cfa21018c3153a53bddc198115e5

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