test: Fix intermittent feature_taproot issue

The transaction is too large to fit into the mempool, so put it into a
block.

https://travis-ci.org/github/bitcoin/bitcoin/jobs/740987240#L7217

test  2020-11-03T01:31:08.645000Z TestFramework (ERROR): JSONRPC error
        Traceback (most recent call last):
          File "./test/functional/test_framework/test_framework.py", line 126, in main
            self.run_test()
          File "./test/functional/feature_taproot.py", line 1448, in run_test
            self.nodes[1].sendtoaddress(address=addr, amount=int(self.nodes[1].getbalance() * 70000000) / 100000000)
          File "./test/functional/test_framework/coverage.py", line 47, in __call__
            return_val = self.auth_service_proxy_instance.__call__(*args, **kwargs)
          File "./test/functional/test_framework/authproxy.py", line 146, in __call__
            raise JSONRPCException(response['error'], status)
        test_framework.authproxy.JSONRPCException: Transaction too large (-6)

Author: MarcoFalke

test/functional/feature_taproot.py

@@ -9,6 +9,7 @@
     create_block,
     add_witness_commitment,
     MAX_BLOCK_SIGOPS_WEIGHT,
+    NORMAL_GBT_REQUEST_PARAMS,
     WITNESS_SCALE_FACTOR,
 )
 from test_framework.messages import (
@@ -1443,10 +1444,22 @@ def run_test(self):
         self.nodes[1].generate(101)
         self.test_spenders(self.nodes[1], spenders_taproot_active(), input_counts=[1, 2, 2, 2, 2, 3])
 
-        # Transfer % of funds to pre-taproot node.
+        # Transfer funds to pre-taproot node.
         addr = self.nodes[0].getnewaddress()
-        self.nodes[1].sendtoaddress(address=addr, amount=int(self.nodes[1].getbalance() * 70000000) / 100000000)
-        self.nodes[1].generate(1)
+        rawtx = self.nodes[1].createrawtransaction(
+            inputs=[{
+                'txid': i['txid'],
+                'vout': i['vout']
+            } for i in self.nodes[1].listunspent()],
+            outputs={addr: self.nodes[1].getbalance()},
+        )
+        rawtx = self.nodes[1].signrawtransactionwithwallet(rawtx)['hex']
+        # Transaction is too large to fit into the mempool, so put it into a block
+        block = create_block(tmpl=self.nodes[1].getblocktemplate(NORMAL_GBT_REQUEST_PARAMS), txlist=[rawtx])
+        add_witness_commitment(block)
+        block.rehash()
+        block.solve()
+        assert_equal(None, self.nodes[1].submitblock(block.serialize().hex()))
         self.sync_blocks()
 
         # Pre-taproot activation tests.