Add Hue to cluster on hmaster01:

* The XML config additions are as prescribed by Cloudera docs.
* Hue itself is apt-installed and the default hue.ini file changed to reflect cluster set-up
* Pulled the symlinking of JDBC driver into its own role ‘postgresql_jdbc_for_hive’,
  because the Hive config needs to be run on both the hive_metastore machine and
  the hue_server machine, but the hue_server won’t have the JDBC driver installed
  (currently part of the postgresql_server role).
* Tagged some Hive tasks with ‘hue’, too, because the main use of Hue is to
  run Hive queries. This could be changed back though.