Declare namenode directory only once

The namenode's base directory was declared in both

  /etc/puppet/manifests/role/analytics/hadoop.pp:280
  /etc/puppet/modules/cdh/manifests/hadoop/namenode.pp:36

which made puppet fail with “Duplicate declaration”. We drop the
role's definition of it, as the directory is only needed on namenodes
anyways.

Change-Id: I8a5a6de00731af2dadb8ab2b3d36ad43faf2f49c