Altair validator client and HTTP API (#2404)

## Proposed Changes

* Implement the validator client and HTTP API changes necessary to support Altair


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

scripts/local_testnet/beacon_node.sh

@@ -20,4 +20,5 @@ exec lighthouse \
 	--enr-udp-port $2 \
 	--enr-tcp-port $2 \
 	--port $2 \
-	--http-port $3
+	--http-port $3 \
+	--target-peers $((NODE_COUNT - 1))

scripts/local_testnet/setup.sh

@@ -9,6 +9,8 @@
 # $VALIDATOR_COUNT and $NODE_COUNT variables.
 #
 
+set -o nounset -o errexit -o pipefail
+
 source ./vars.env
 
 lcli \
@@ -20,10 +22,9 @@ lcli \
 NOW=`date +%s`
 GENESIS_TIME=`expr $NOW + $GENESIS_DELAY`
 
-
 lcli \
-	--spec mainnet \
 	new-testnet \
+	--spec $SPEC_PRESET \
 	--deposit-contract-address $DEPOSIT_CONTRACT_ADDRESS \
 	--testnet-dir $TESTNET_DIR \
 	--min-genesis-active-validator-count $GENESIS_VALIDATOR_COUNT \
@@ -50,8 +51,8 @@ echo Validators generated with keystore passwords at $DATADIR.
 echo "Building genesis state... (this might take a while)"
 
 lcli \
-	--spec mainnet \
 	interop-genesis \
+	--spec $SPEC_PRESET \
 	--genesis-time $GENESIS_TIME \
 	--testnet-dir $TESTNET_DIR \
 	$GENESIS_VALIDATOR_COUNT

scripts/local_testnet/vars.env

@@ -29,6 +29,9 @@ NETWORK_ID=4242
 # Hard fork configuration
 ALTAIR_FORK_EPOCH=18446744073709551615
 
+# Spec version (mainnet or minimal)
+SPEC_PRESET=mainnet
+
 # Seconds per Eth2 slot
 SECONDS_PER_SLOT=3