Test eth RPC interface for the light client.

[dvdplm]

Currently there are no tests for RPC calls against the light client and there is a significant amount of logic to manage requests.
The tests for the full client require a fair amount of setup and the difference in style of implementation means that replicating that for the light client RPC calls could be a significant chunk of work.

Can/should some of this logic be moved from the rpc crate into ethcore/light? It is possible that using the existing testing helpers in ethcore/light will make it easier to achieve proper test coverage.

The background to this issue is a panic-bug that was caused by an off-by-one mistake in the rpc crate when setting up requests for an eth_getBlockByHash RPC call: finding the bug was harder than expected and adding a test for it even more so (hence this ticket here).

[rphmeier]

We should be able to mock the OnDemand service completely for the light client RPCs. IMO that would work better than actually trying to set up a dummy network to request data from.

[adria0]

Closing issue due to its stale state.