Add `hive-server` option to send filled fixtures to a server

[marioevz]

Add an option to send the blockchain fixtures via RPC to the pyspec hive simulator running in a "server" mode.

We currently have pyspec simulator in hive, which contains a single pyspec suite that runs all tests by fetching them from the latest release in this repo.

We could add a second suite called server that has a single test which spawns up a server that listens for calls at a given endpoint where it receives the blockchain tests to run.

For each test received through this endpoint, the server runs a new test with all available execution clients and reports the outcome.

Hive command:

./hive --client-file ./configs/cancun.yaml --client ethereumjs --sim ethereum/pyspec --sim.limit "server/"

Execution-spec-tests command:

fill --until=Cancun --enable-hive --hive-server=http://172.25.0.3:8080/