Load ethereum private key

Load an ethereum keystore when the node is started in coordinator mode.  The
private key corresponding to the forger address must be imported into the
keystore before running the node in coordinator mode.  You can see an examples
in `cli/node/load-sk-example.sh`.

config/config.go

@@ -83,6 +83,10 @@ type Coordinator struct {
 		// AttemptsDelay is delay between attempts do do an eth client
 		// RPC call
 		AttemptsDelay Duration `validate:"required"`
+		Keystore      struct {
+			Path     string `validate:"required"`
+			Password string `validate:"required"`
+		} `validate:"required"`
 	} `validate:"required"`
 	API struct {
 		Coordinator bool
@@ -91,6 +95,9 @@ type Coordinator struct {
 		// BatchPath if set, specifies the path where batchInfo is stored
 		// in JSON in every step/update of the pipeline
 		BatchPath string
+		// LightScrypt if set, uses light parameters for the ethereum
+		// keystore encryption algorithm.
+		LightScrypt bool
 	}
 }