Support masking the WRITE_SYNC latency from ChronologyProtector

Support masking the WRITE_SYNC latency from ChronologyProtector

* Use OutputPage::output() as the method to mask latency, since it
  takes a good while to run. By the time it runs, cache replication
  should have caught up, so the reap call will likely not block.
* For redirects emitted after changes in POST, instead of masking
  with OutputPage, add a parameter to the redirect and block on
  the positions appearing. This uses the redirection RTT to mask
  the replication latency.

Change-Id: Ib23690c302e8033610fef9a0ef451dafe8a5803e