Fixes RestHelper and IndexTemplateCluster test for backport #1885: opendistro-1.12

[rutuja-amazon]

Fixes for RestHelper.java and IndexTemplateClusterPermissionsCheckTest.java for #1986

Description

Fixes backport of #1885

Issues Resolved

Backport PR #1885

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed per the DCO using --signoff

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[peternied]

After much consideration and discussion the branch that is being targeted opendistro-1.1* is unsupported, and this code is being used and maintained by a private fork. Rather than gate changes to a fork, it makes more sense for that repository to diverge in the areas its supporting but this repository are not supporting. This avoids having to wait on the security maintainers to review / approve / merge changes - doubly so when these changes cannot be validated by the CI systems in GitHub associated with them.

I am closing out this pull request and the other related pull requests, separately we will consider how we want to address these branches that are no longer supported, in other OpenSearch Project components the ODFE versions of the codebases were archived whereas this one was copied with all its issues.