test: introduce generate_to_height helper, use in rpc_signrawtransaction

This will speed up the test a bit and avoid potential .generate() RPC
timeouts (in sub-test `test_signing_with_cltv()`) on slower machines.

test/functional/rpc_signrawtransaction.py

@@ -15,6 +15,7 @@ from test_framework.util import (
     assert_equal,
     assert_raises_rpc_error,
     find_vout_for_address,
+    generate_to_height,
     hex_str_to_bytes,
 )
 from test_framework.messages import (
@@ -270,7 +271,7 @@ class SignRawTransactionsTest(BitcoinTestFramework):
         getcontext().prec = 8
 
         # Make sure CSV is active
-        self.nodes[0].generate(500)
+        generate_to_height(self.nodes[0], 500)
         assert self.nodes[0].getblockchaininfo()['softforks']['csv']['active']
 
         # Create a P2WSH script with CSV
@@ -306,7 +307,7 @@ class SignRawTransactionsTest(BitcoinTestFramework):
         getcontext().prec = 8
 
         # Make sure CLTV is active
-        self.nodes[0].generate(1500)
+        generate_to_height(self.nodes[0], 1500)
         assert self.nodes[0].getblockchaininfo()['softforks']['bip65']['active']
 
         # Create a P2WSH script with CLTV

test/functional/test_framework/util.py

@@ -559,6 +559,17 @@ def mine_large_block(node, utxos=None):
     node.generate(1)
 
 
+def generate_to_height(node, target_height):
+    """Generates blocks until a given target block height has been reached.
+       To prevent timeouts, only up to 200 blocks are generated per RPC call.
+       Can be used to activate certain soft-forks (e.g. CSV, CLTV)."""
+    current_height = node.getblockcount()
+    while current_height < target_height:
+        nblocks = min(200, target_height - current_height)
+        current_height += len(node.generate(nblocks))
+    assert_equal(node.getblockcount(), target_height)
+
+
 def find_vout_for_address(node, txid, addr):
     """
     Locate the vout index of the given transaction sending to the