BIGTOP-2603: NN/RM charm should include a spark user/group

[kwmonroe]

When NN/RM are not colocated with spark, they do not know about the spark user/group. When in yarn-client mode, the spark charm will create hdfs dirs with spark ACLs. This leads to warnings like this on the namenode:

WARN org.apache.hadoop.security.UserGroupInformation: No groups available for user spark

Always create the spark user/group on NN and RM. This also works if spark/NN/RM are all colocated.

Note that hadoop should be a secondary group (not primary) for extra users created by these charms, so this PR ensures that as well.

[ktsakalozos]

LGTM +1 . Do you think we should be doing the same with other components that may use hdfs, like hbase?

[kwmonroe]

Yeah, we probably should. oozie and hue come to mind. We chatted about this a little while ago. It would really be nice if the charm that relied on hadoop-plugin would send user info over the plugin relation.

The plugin would then proxy that to the NN or RM as needed. Unfortunately, this isn't really a priority at the moment, so I think we'll treat spark as special for now and work up a more generic solution later.