upgrade logstash-filters-common -> 16
Add elasticsearch drain script

This takes care of disabling allocations during restarts (to avoid unnecessary
rebalancing while its offline) and moving shards off a host (if it's bing shut
down permanently).

This is disabled by default so we can do more intentional testing with it.
re-include some default elasticsearch exec options (forgot some were not logging-related) from /commit 6df1932fcb /issue #55