simplify repl scheduled fs test

This is a refactored version of the repl scheduled fullsync test to deal with reliability problems. There doesn't seem to be a great way to test scheduling, so this is what you get.

- the test doesn't write any data, it just checks "scheduling" (yeah, "scheduling" in double quotes)
- use intercepts to check for a # of minutes to wait, but don't actually sleep
  - check invariants in the intercept:
    - FS to cluster B should always be 1 minute
    - FS to cluster C should always be 2 minutes
    - FS to all clusters (ie, not specified in repl config) should be 99 minutes
- ring size changed to 4 to speedup fs