Rename random to prev_randao (#3040)

## Issue Addressed

As discussed on last-night's consensus call, the testnets next week will target the [Kiln Spec v2](https://hackmd.io/@n0ble/kiln-spec).

Presently, we support Kiln V1. V2 is backwards compatible, except for renaming `random` to `prev_randao` in:

- https://github.com/ethereum/execution-apis/pull/180
- https://github.com/ethereum/consensus-specs/pull/2835

With this PR we'll no longer be compatible with the existing Kintsugi and Kiln testnets, however we'll be ready for the testnets next week. I raised this breaking change in the call last night, we are all keen to move forward and break things.

We now target the [`merge-kiln-v2`](https://github.com/MariusVanDerWijden/go-ethereum/tree/merge-kiln-v2) branch for interop with Geth. This required adding the `--http.aauthport` to the tester to avoid a port conflict at startup.

### Changes to exec integration tests

There's some change in the `merge-kiln-v2` version of Geth that means it can't compile on a vanilla Github runner. Bumping the `go` version on the runner solved this issue.

Whilst addressing this, I refactored the `testing/execution_integration` crate to be a *binary* rather than a *library* with tests. This means that we don't need to run the `build.rs` and build Geth whenever someone runs `make lint` or `make test-release`. This is nice for everyday users, but it's also nice for CI so that we can have a specific runner for these tests and we don't need to ensure *all* runners support everything required to build all execution clients.

## More Info

- [x] ~~EF tests are failing since the rename has broken some tests that reference the old field name. I have been told there will be new tests released in the coming days (25/02/22 or 26/02/22).~~

testing/execution_engine_integration/src/main.rs

@@ -0,0 +1,28 @@
+/// This binary runs integration tests between Lighthouse and execution engines.
+///
+/// It will first attempt to build any supported integration clients, then it will run tests.
+///
+/// A return code of `0` indicates the tests succeeded.
+mod build_geth;
+mod execution_engine;
+mod genesis_json;
+mod test_rig;
+
+use execution_engine::Geth;
+use test_rig::TestRig;
+
+/// Set to `false` to send logs to the console during tests. Logs are useful when debugging.
+const SUPPRESS_LOGS: bool = false;
+
+fn main() {
+    if cfg!(windows) {
+        panic!("windows is not supported, only linux");
+    }
+
+    test_geth()
+}
+
+fn test_geth() {
+    build_geth::build();
+    TestRig::new(Geth).perform_tests_blocking();
+}