Vanilla Hadoop 2 plugin can't start HDFS service only

[Alexander Ignatov]

Steps to reproduce:
1) Create two node groups:
     worker - 'datanode' process only
     master - 'namenode' process only
2) Try to create cluster using node groups above.

Expected result:
Cluster has been started successfully. Provisioned HDFS service is operable.

Actual result:
Provisioning fails because plugin assumes that resource manager service is in some node group processes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/96371

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/96371
Committed: https://git.openstack.org/cgit/openstack/sahara/commit/?id=c03dd4f4e4b86e4868b2a4a803218ed38d5dd698
Submitter: Jenkins
Branch: master

commit c03dd4f4e4b86e4868b2a4a803218ed38d5dd698
Author: Alexander Ignatov <email address hidden>
Date: Thu May 29 10:18:08 2014 +0400

    Added ability to run HDFS service only with Hadoop 2

    * Now Sahara provision YARN and MapReduce configs only when user
      selected appropriate processes in node groups

    * Extracted getting hostnames of provisioned services to separate
      method in plugin utils

    Change-Id: I2819c05201e6b35e4e5c8e810d243cb0b271073f
    Closes-Bug: #1324383