Fix typo in log aggregation settings

Log aggregation did not work, as the template tried to set

  yarn.log.aggregation.enable

(3 dots) although yarn checks for

  yarn.log-aggregation-enable

(1 dot, two dashes). So we switch to using the latter setting to get
log aggregation to work.

See:
  http://hadoop.apache.org/docs/r2.3.0/hadoop-yarn/hadoop-yarn-common/yarn-default.xml

Change-Id: Ibae2ffd35951cce925cfeef97c46024001d692c7