Faster check for clash
Faster check for clash

- Use user_sessions when checking for clash.
- Removed setUserSessions Function and associated
  functions. Had to run those scripts locally due
  to time and memory constraints of Functions.
- Update reservation cutoff time to 1 hour before
  start of session.
Change-Id: I39fd44b44f802146bd25adcc91c00578910db5e0

google/iosched,google/iosched,google/iosched