Properly escape Windows paths when creating new files.
Properly escape Windows paths when creating new files.

This was why Windows swarm bots were failing to restart after updates.

TBR=maruel@chromium.org
BUG=

Review URL: https://codereview.appspot.com/44990046

madecoste/swarming,pombreda/swarming,luci/luci-py,luci/luci-py,luci/luci-py,madecoste/swarming,pombreda/swarming,madecoste/swarming,madecoste/swarming,pombreda/swarming,luci/luci-py,pombreda/swarming