Add proposer slashing support to test_harness

Test harness will now add signatures to a ProposerSlashing and submit it
to the BeaconChain

beacon_node/beacon_chain/test_harness/examples/chain.yaml

@@ -19,6 +19,17 @@ test_cases:
         - slot: 5
           amount: 32
           merkle_index: 2
+      proposer_slashings:
+        - slot: 8 # At slot 8, we trigger a proposal slashing occurring
+          proposer_index: 42 # We penalize the validator at position 42
+          proposal_1_shard: 0
+          proposal_1_slot: 15
+          proposal_1_root: !!binary |
+            LkmqmqoodLKAslkjdkajsdljasdkajlksjdasldjasdd
+          proposal_2_shard: 0
+          proposal_2_slot: 15
+          proposal_2_root: !!binary |
+            DIFFERENTKAslkjdkajsdljasdkajlksjdasldjasdd
     results:
       num_validators: 1000
   - config: