NIFI-2655 Handle absence of -n/-l flag for encrypt-config.sh

[alopresto]

This PR is already rebased against PR 1261 so it should not be merged to master until after that PR is merged. Once that occurs, this PR will drop to a much smaller changeset.

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[alopresto]

I rebased this after PR 1261 was merged to master. Ready for review.