Change announcement ID to a UUID instead of Timestamp (#1221 backport)

* Use "_" instead of "-"

* Also add a UUIDUtils to the common package

Conflicts:
	server/src/test/java/io/druid/client/client/BatchServerInventoryViewTest.java

Backport #1161: Fix to maintain correctness when out-of-order ZK updates are received

on receiving ZK ADD/UPDATE events, get latest data from zookeeper instead of taking it from the event which might be stale due to event coming out of order etc

fix documentation of default value for druid.coordinator.merge.on on 0.6.x branch

Backport Dynamic configuration fixes for worker select strategy

- Create local firehose files in a clean temp directory to avoid
firehose reading other random temp files that start with 'druid'

Conflicts:
	indexing-service/src/test/java/io/druid/indexing/common/task/IndexTaskTest.java

Default to UTF-8 on MySQL

ensure utf-8 db before the next release

Add a conversion script to convert old and new ingestion specs

add travis-ci config