do not spend coinbase

as of now, we don't retry mining keystones if they fail.  in e2e tests we only check that 1 keystone was mined, if this fails, then the test fails.  make this highly unlikely by doing two things:
* generating a lot of blocks, 300 to start, 100 every second
* don't check the same keystone for mining, check every keystone, this is an e2e test; if one was mined it passes

fixes #2

e2e/network_test.go

@@ -215,13 +215,15 @@ func TestFullNetwork(t *testing.T) {
 	go func() {
 		// create a new block every second, then view pop payouts and finalities
 
-		firstL2Keystone := hemi.L2KeystoneAbbreviate(l2Keystone).Serialize()
+		keystones := []hemi.L2Keystone{}
 
 		for {
 			l2KeystoneRequest := bssapi.L2KeystoneRequest{
 				L2Keystone: l2Keystone,
 			}
 
+			keystones = append(keystones, l2Keystone)
+
 			err = bssapi.Write(ctx, bws.conn, "someid", l2KeystoneRequest)
 			if err != nil {
 				t.Logf("error: %s", err)
@@ -237,7 +239,7 @@ func TestFullNetwork(t *testing.T) {
 					"-rpcuser=user",
 					"-rpcpassword=password",
 					"generatetoaddress",
-					"1",
+					"100", // generate a bunch so we're less likely to spend coinbase
 					btcAddress.EncodeAddress(),
 				},
 			)
@@ -251,20 +253,15 @@ func TestFullNetwork(t *testing.T) {
 
 			time.Sleep(1 * time.Second)
 
-			err = bssapi.Write(ctx, bws.conn, "someotherid", bssapi.PopPayoutsRequest{
-				L2BlockForPayout: firstL2Keystone[:],
-			})
-			if err != nil {
-				t.Logf("error: %s", err)
-				return
-			}
-
-			err = bssapi.Write(ctx, bws.conn, "someotheridz", bssapi.BTCFinalityByRecentKeystonesRequest{
-				NumRecentKeystones: 100,
-			})
-			if err != nil {
-				t.Logf("error: %s", err)
-				return
+			for _, keystone := range keystones {
+				ks := hemi.L2KeystoneAbbreviate(keystone).Serialize()
+				err = bssapi.Write(ctx, bws.conn, "someotherid", bssapi.PopPayoutsRequest{
+					L2BlockForPayout: ks[:],
+				})
+				if err != nil {
+					t.Logf("error: %s", err)
+					return
+				}
 			}
 		}
 	}()