Basic backwards compatibility support for watcher.
Closeselastic/elasticsearch#3230
Relates to elastic/elasticsearch#3231 - this actually should fix all the failures caused
by fractional time values but it does so by being able to parse them.
Being able to parse them is important for 2.x compatibility but 5.0
watches shouldn't produce fractional time values. This fixes the
particular way of making fractional time values mentioned in elastic/elasticsearch#3231
but I expect there are a half dozen more places to fix. The actual
watcher tests are fairly basic.
Original commit: elastic/x-pack-elasticsearch@328717455c
The actual backwards compatibility support is handled by core's ability to downgrade `keyword` and `text` into `string` for indexes created in 2.x.
Original commit: elastic/x-pack-elasticsearch@6b615d9a45
Nik Everett