Add RPC integration tests

[TDemeco]

Quote from PR #416, for futurte reference:
We should strive for this option: adding an rpc integration test suite like we have for bsp, msp, etc. It's going to be useful to:

• Test all the functionality added in this PR (by running an FTP server, an HTTP one, and test access to local paths)
• Test access control using CORS for all RPC methods to make sure they can't be used by bad actors
• Test the already existing RPC methods
• Test any new RPC methods that we add along the way

Originally posted by @TDemeco in #416 (comment)

[Karrq]

What do you think of #427?

Still working on it, discovered an issue with HTTP download FIXED :)