NIFI-4343 - allow multiple URLs in SiteToSite reporting tasks

[pvillard31]

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[ijokarumawak]

@pvillard31 I looked at the change briefly. I think we also need to change to use new SiteToSiteClient.Builder().urls() instead of url() here:
https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-site-to-site-reporting-bundle/nifi-site-to-site-reporting-task/src/main/java/org/apache/nifi/reporting/AbstractSiteToSiteReportingTask.java#L193

[pvillard31]

Good catch @ijokarumawak and thanks for the review. Just pushed a commit to address your comment.

[ijokarumawak]

This change just reminded me that SiteToSiteRestApiClient.parseClusterUrls also validates the destinationUrl. Probably it'd be a better approach to use SiteToSiteRestApiClient.parseClusterUrls and catch IllegalArgumentException from NiFiUrlValidator.validate(), instead of implementing different validation code there. How do you think?

[pvillard31]

Realizing that this method is adding /nifi-api (or converting /nifi into /nifi-api). I changed the validator and updated the unit test accordingly.

[ijokarumawak]

@pvillard31 Thanks for the update. I've confirmed that SiteToSiteProvenanceReportingTask can use comma separated URLs, and stay being able to send events even if one of the remote NiFi instances specified at the URLs went down, and also the reporting task can resume sending while the remote node was down, by establishing S2S connection with other available node.

LGTM +1, I'm going to squash commits and merge to master. Thank you!