Problem: json-rpc failed on pruned nodes (backport #550)

[yihuang]

Solution:

• Make basic json-rpc apis works on pruned nodes
• Test with integration tests

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• Have you read the CONTRIBUTING.md?
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• Have you included tests for any non-trivial functionality?
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Thank you for your code, it's appreciated! :)

[adu-crypto]

typo in comment, others lgtm