HDFS-1150: Comment and review

[Jakob Homan]

HDFS-1150 (https://issues.apache.org/jira/browse/Hdfs-1150), part of the 
security initiative, is a rather big change to the way Datanodes are 
started in a secure environment and the resources needed to start one. 
I want to make sure the community gets a chance to review the approach 
we're taking - and the rather innocuous title may not convey the change 
we're looking at.

The jsvc approach we've taken  appears to be working and we're going to 
commit it to the Y20 branch, but more comments are certainly welcome.

-Jakob
Hadoop @ Yahoo!