[tests] allow tests to be run with --usecli

test_framework accepts a new --usecli parameter. Running the test with
this parameter will cause all RPCs to be sent through bitcoin-cli rather
than directly over http. By default, individual test cases do not
support --usecli, and self.supports_cli must be set to True in the
set_test_params method.

We can make supports_cli default to True in future once we know which
tests will fail with use_cli.

test/functional/create_cache.py

@@ -16,6 +16,7 @@ class CreateCache(BitcoinTestFramework):
 
     def set_test_params(self):
         self.num_nodes = 0
+        self.supports_cli = True
 
     def setup_network(self):
         pass