qa: Extract rpc_timewait as test param

Also increase it for wallet_dump and wallet_groups

test/functional/wallet_groups.py

@@ -22,6 +22,7 @@ class WalletGroupTest(BitcoinTestFramework):
         self.setup_clean_chain = True
         self.num_nodes = 3
         self.extra_args = [[], [], ['-avoidpartialspends']]
+        self.rpc_timewait = 120
 
     def run_test (self):
         # Mine some coins