Currently Ambari does not support the definition of multiple Nameservices. It is always assumed hdfs_site['dfs.nameservices'] is just a string defining one nameservice.
Multiple nameservices can be configured for exmaple to support seamless distcp between two HA clusters. The nameservices are defined as a comma separated list in hdfs_site['dfs.nameservices'].
This patch introduces the method get_nameservice(hdfs_site), which splits the value into in an array and identifies the nameservice for the current cluster with what is set in hdfs_site['dfs.namenode.shared.edits.dir']. By default the first nameservice is returned or empty.
To verify the current namservice it would be preferred to use fs.defaultFS in core-site, but getting this config into namenode_ha_utils.py seems more involved.