Fixed bugs in Elasticstack and EC2 drivers

This pull requests addresses the following issues:
EC2 multiple region drivers issue: https://issues.apache.org/jira/browse/LIBCLOUD-583
Elastichost response parse error: https://issues.apache.org/jira/browse/LIBCLOUD-584
Elastichost invalid IP field name: https://issues.apache.org/jira/browse/LIBCLOUD-585