Doppelganger detection (#2230)

## Issue Addressed

Resolves #2069 

## Proposed Changes

- Adds a `--doppelganger-detection` flag
- Adds a `lighthouse/seen_validators` endpoint, which will make it so the lighthouse VC is not interopable with other client beacon nodes if the `--doppelganger-detection` flag is used, but hopefully this will become standardized. Relevant Eth2 API repo issue: https://github.com/ethereum/eth2.0-APIs/issues/64
- If the `--doppelganger-detection` flag is used, the VC will wait until the beacon node is synced, and then wait an additional 2 epochs. The reason for this is to make sure the beacon node is able to subscribe to the subnets our validators should be attesting on. I think an alternative would be to have the beacon node subscribe to all subnets for 2+ epochs on startup by default.

## Additional Info

I'd like to add tests and would appreciate feedback. 

TODO:  handle validators started via the API, potentially make this default behavior

Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
Co-authored-by: Paul Hauner <paul@paulhauner.com>

scripts/local_testnet/README.md

@@ -20,7 +20,7 @@ Start a local eth1 ganache server
 ./ganache_test_node.sh
 ```
 
-Assuming you are happy with the configuration in `var.env`, deploy the deposit contract, make deposits, 
+Assuming you are happy with the configuration in `var.env`, deploy the deposit contract, make deposits,
 create the testnet directory, genesis state and validator keys with:
 
 ```bash

scripts/local_testnet/bootnode.sh

@@ -30,4 +30,4 @@ exec lighthouse boot_node \
     --testnet-dir $TESTNET_DIR \
     --port $BOOTNODE_PORT \
     --listen-address 127.0.0.1 \
-    --network-dir $DATADIR/bootnode \
+    --network-dir $DATADIR/bootnode \

scripts/local_testnet/ganache_test_node.sh

@@ -2,12 +2,12 @@
 
 source ./vars.env
 
-ganache-cli \
+exec ganache-cli \
 	--defaultBalanceEther 1000000000 \
 	--gasLimit 1000000000 \
 	--accounts 10 \
 	--mnemonic "$ETH1_NETWORK_MNEMONIC" \
 	--port 8545 \
-	--blockTime 3 \
+	--blockTime $SECONDS_PER_ETH1_BLOCK \
 	--networkId "$NETWORK_ID" \
 	--chainId "$NETWORK_ID"

scripts/local_testnet/setup.sh

@@ -33,7 +33,8 @@ lcli \
 	--altair-fork-epoch $ALTAIR_FORK_EPOCH \
 	--eth1-id $NETWORK_ID \
 	--eth1-follow-distance 1 \
-	--seconds-per-eth1-block 1 \
+	--seconds-per-slot $SECONDS_PER_SLOT \
+	--seconds-per-eth1-block $SECONDS_PER_ETH1_BLOCK \
 	--force
 
 echo Specification generated at $TESTNET_DIR.

scripts/local_testnet/validator_client.sh

@@ -16,4 +16,5 @@ exec lighthouse \
 	--datadir $1 \
 	--testnet-dir $TESTNET_DIR \
 	--init-slashing-protection \
-	--beacon-nodes $2
+	--beacon-nodes $2 \
+	$VC_ARGS

scripts/local_testnet/vars.env

@@ -28,3 +28,9 @@ NETWORK_ID=4242
 
 # Hard fork configuration
 ALTAIR_FORK_EPOCH=18446744073709551615
+
+# Seconds per Eth2 slot
+SECONDS_PER_SLOT=3
+
+# Seconds per Eth1 block
+SECONDS_PER_ETH1_BLOCK=1