RPC compatiblity testing

[lemmih]

Issue summary

Notes and thoughts.

We want to verify that Forest is syntactically compatible with a known subset of the Lotus RPC calls. This means our requests/response pairs follow the same JSON schema. We also want to verify that our responses are sensible. Exactly what this means depends on the RPC call in question, unfortunately.

We can assert that blockchain-related RPC calls return exactly the same as their Lotus counterpart (for example, ChainGetTipSetByHeight must return the same answer in both Forest and Lotus). Non-blockchain RPC calls (such as MpoolPending) are more difficult to test, and we may settle for merely testing the JSON schema.

Other information and links

Using glif.io for compatibility testing isn't ideal since they do not give access to several important RPC methods.