Use Spark public DNS if available to report Flow UI

[exalate-issue-sync]

If spark env variable SPARK_PUBLIC_DNS is defined, then we should use it to report Flow UI address.

[exalate-issue-sync]

Jakub Hava commented: If I understand it correctly, we want to hide ip address h2o cluster is using and in case public dns name is set, use that. See the tiny commit if this is what we're looking for

This therefore also implements https://0xdata.atlassian.net/projects/SW/issues/SW-338?filter=allopenissues

[DinukaH2O]

JIRA Issue Migration Info

Jira Issue: SW-344
Assignee: Jakub Hava
Reporter: Michal Malohlava
State: Resolved
Fix Version: 1.6.9
Attachments: N/A
Development PRs: N/A

[hasithjp]

JIRA Issue Migration Info Cont'd

Jira Issue Created Date: 2017-03-06T17:20:55.724-0800