Update site xml with Generated value

[bijugs]

For e.g. here

site_xml = node['bcpc']['hadoop']['hbase']['site_xml']
complete_hbase_site_hash = generated_values.merge(site_xml)

should be

site_xml = node['bcpc']['hadoop']['hbase']['site_xml']
complete_hbase_site_hash = site_xml.merge(generated_values)

so that if there are any duplicates then value from generated_values in the recipe will be used.

[vt0r]

Warning: This reverses the prior behavior of site_xml being of higher precedence, as described above and in the PR. I'd assume most of us expect to be able to add or override individual config params/values in the environment by adding site_xml options. On items that didn't exist previously, this will still work as expected, but overriding existing values will no longer work.

We should definitely discuss whether this was the intended result, and if so, we will need to add some means of overriding existing parameters.