feat(db) upstreams and targets to new dao (replaces #3622 and #3660)

[bungle]

The new admin API is fairly similar to the previously existing one, but there are some breaking changes:

• Lists (GET /upstreams or GET /upstreams/{upstream}/targets) don't accept query-attributes for filtering any more
• Pagination: the total attribute is gone
• Format of error messages has changed to new DAO errors.
• PUT actions now are applied to entities instead of to collections. (PUT /upstreams/foo instead of PUT /upstreams
• Some error codes have changed:
  • Attempting to use an invalid name name (such an IP address) when updating an upstream has become a 500 error instead of a 400.
  • PUT actions return a 200 on creation instead of 201.
• timestamps (like created_at) can be presented and stored either with seconds or milliseconds resolution

New features:

• There is a attribute called next on paginated admin API results.
• When listing the targets for an upstream with db.targets:for_upstream(u), the list only includes active targets, and is reverse-sorted by created_at+id. This is the method used in /upstreams/{upstream}/targets
• There is also a db.targets:for_upstreams_raw(u) which returns all targets, including those with weight=0, associated with the upstream. That's what used in /upstreams/{upstream}/targets/all
• db.targets:for_upstream_with_health(u) is the same list as db.targets:for_upstream(u) but also includes health information (so it is slower to call). It is used in /upstreams/{upstream}/health.
• In addition to those there's db.targets:for_upstream_sorted(u) which returns the targets sorted by created_at+id. It is used internally in a couple places for things like cleaning up and building the cache.
• The db.targets:delete method creates a new target with weight = 0. The only way to really delete a target from the database is by inserting targets (this will eventually trigger a clean_history call).
• The the db.targets:post_health is the one-place for changing health status of a target. It deals with balancer changes and sending events to the cluster. It is used in POST /upstreams/{upstream}/targets/{target}/healthy|unhealthy.

Prerequisites:

• Cassandra migrations where not re-entrant (they can not "catch exceptions and continue" like postgres can). In the past the tests where run only in postgresql. I had to add a way to "ignore errors" in order to allow re-entrant migrations in Cassandra.
• There was a lurking bug related with partial updates of record-type fields.
• Needed a new kind of validator to allow validating the hash_on_header is not equal to hash_fallback_header
• The target.target attribute is an endpoint key but it is not unique. Had to remove that restriction from the system.
• Timestamps should have option for millisecond-precision, but until we updated the targets to the new DAO we didn't see need for that (it is added as an option, and targets entity uses milliseconds precision)

This PR replaces #3622 and #3660.

[hishamhm]

all these lines containing uppercase DEBUG logs (plus the print below) should be removed

[hishamhm]

this is also a leftover