Make WANObjectCache sets account for slave lag

Make WANObjectCache sets account for slave lag

* This gets lag information that is useful when
  the calling code is about to run queries that
  will have their results cached.
* This is now used in place of trxTimestamp() for
  WANObjectCache set() and getWithSetCallback().
* The WAN cache will use a low TTL if the lag is
  too high to avoid caching stale data for weeks.
* Bumped MAX_COMMIT_DELAY as nothing enforces it.

Bug: T113204
Change-Id: I2a95b4088cff42d6e980351555f81a4b13519e24