Azkaban 3.0.0: Multiple Executor Support, Execute job as user, Java 1.8 and more..

Improve scalability through supporting multiple exec servers #439
Merging execute-as-user into Azkaban 3 #56
Use Guava Cache implementation #552
Run CI against both JDK 7 and 8 #547
Move DirectoryFlowLoader from azkaban.util to azkaban.project #520
Use error-prone for better compile-time analysis #501
Auto upgrade database up to database.properties version and track draining flows #491
Issue #483 - Exclude Cipher Suites with Logjam vulnerability

Please refer to latest documentation for details.