[oozie] improve support for 2.1 images

[cjac]

This PR includes updates that we've found improve the experience for some of our customers.

• declare master_node and ROLE variables in header
• define sample secret name to provide more complete defaults
• create function await_hdfs_datanodes to pause for quorum
• only interact with dfs if quorum has been reached
• moved oozie.service.ProxyUserService.proxyuser.oozie.* property definitions down a few lines
• called out whitepaper recommending these properties
• purge local guava jar and replace it with octets from an https url

[cjac]

continuation of #1078

[cjac]

/gcbrun