Replication auto_check for nextgenrepl full-sync

[martinsumner]

The nextgenrepl aae full-sync supports a schedule of checks, where each type of check has a different scope:

• all_check: Full-check over all time;
• day_check: Check over the previous day only;
• hour_check: Check over the previous hour only;
• range_check: Check if and only if a previous check had highlighted a time range over which to constrain results;
• no_check: Don't check.

The enhancement is to offer a further check type - auto_check:

• auto_check: If a range has been discovered, perform a range_check, otherwise if the current time is within the all_check_window perform an all_check, otherwise perform a day_check.

The all_check_window will consist of a start hour (0 to 23) and an end hour (0 to 23). So setting the start hour to 23 and the end hour to 6, would prompt all_check between 23:00 and 06:59 and day_check between 07:00 and 22:59 (where a range_check cannot be triggered).

If no window is defined, then auto_check will always use all_check when no range has been discovered.

The default schedule will change for tictac aae full-sync from [{all_check, 24}] to [{auto_check, 24}].

There will be an additional remote_console command to allow for the window to be cleared or reset across the cluster at run-time.

[martinsumner]

From a configuration perspective the window should follow the model of the bitcask merge window.

[martinsumner]

https://github.com/basho/riak_kv/pull/1816