[mining] segwit option must be set in GBT

Calling getblocktemplate without the segwit rule specified is most
likely a client error, since it results in lower fees for the miner.
Prevent this client error by failing getblocktemplate if called without
the segwit rule specified.

test/functional/mining_getblocktemplate_longpoll.py

@@ -15,14 +15,14 @@ class LongpollThread(threading.Thread):
     def __init__(self, node):
         threading.Thread.__init__(self)
         # query current longpollid
-        template = node.getblocktemplate()
+        template = node.getblocktemplate({'rules': ['segwit']})
         self.longpollid = template['longpollid']
         # create a new connection to the node, we can't use the same
         # connection from two threads
         self.node = get_rpc_proxy(node.url, 1, timeout=600, coveragedir=node.coverage_dir)
 
     def run(self):
-        self.node.getblocktemplate({'longpollid':self.longpollid})
+        self.node.getblocktemplate({'longpollid': self.longpollid, 'rules': ['segwit']})
 
 class GetBlockTemplateLPTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -34,10 +34,10 @@ class GetBlockTemplateLPTest(BitcoinTestFramework):
     def run_test(self):
         self.log.info("Warning: this test will take about 70 seconds in the best case. Be patient.")
         self.nodes[0].generate(10)
-        template = self.nodes[0].getblocktemplate()
+        template = self.nodes[0].getblocktemplate({'rules': ['segwit']})
         longpollid = template['longpollid']
         # longpollid should not change between successive invocations if nothing else happens
-        template2 = self.nodes[0].getblocktemplate()
+        template2 = self.nodes[0].getblocktemplate({'rules': ['segwit']})
         assert(template2['longpollid'] == longpollid)
 
         # Test 1: test that the longpolling wait if we do nothing