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.
Partial backport of core PR11970 (commit f6ade9c)
Depends on D2398