Fix task_util dependency and add it to all target.

Reviewed at https://reviews.apache.org/r/28048/
Show update page URL in the output for beta-update start.

Bugs closed: AURORA-766

Reviewed at https://reviews.apache.org/r/28019/
Move zookeeper connection off the main thread to prevent client deadlocks.

Reviewed at https://reviews.apache.org/r/27698/