Allow empty reseller prefixes in domain_remap

Change-Id: I2013e4686fce1c06626ec974f8d721721e6ca6e7
Multithread optimization for object updater

This change makes the object updater work the same
as the container updater, which is that it now
spawns one thread for each node that it needs to
update. This should help optimize its
performance/efficiency.

Change-Id: If740b8c67c0d953e4b510913bd8594570d868da6
authors and changelog updates for 2.1.0 release

Change-Id: I457674f564dcacf0fd20004e9a3bb85113f53aa5
Merge "Multithread optimization for object updater"
Merge "authors and changelog updates for 2.1.0 release"
added Alex to AUTHORS

Change-Id: I2d147415e65c0f19159b995fc4eca78e075537b6
container merge_items speedup

I rewrote ContainerBroker.merge_items to use bulk SQL operations.  This
performs identical to the current version when len(item_list) == 1.  But as
item_list grows, the new version performs better, up to around 50% faster when
item_list numbers in the hundreds.

I wrote a quick script to stress test merge_items:
https://gist.github.com/redbo/12a4ed9c6a020aee39fe

Average of several runs against master: 35.08 seconds
Average of several runs against this branch: 18.44 seconds

Change-Id: I07fff1fb05c90f1411c79d961e0ed63264ed2acf
Merge "container merge_items speedup"
Merge "Allow empty reseller prefixes in domain_remap"
Merge master to feature/ec

Change-Id: Ia98cf267dcafed5c3c67c54e7b9911315e7ad3a8