The current implementation of dtest shim use `server_id` to format a
name of a node in a cluster. This is a difference in behavior with dtest.
Some of dtests use code like `cluster.nodes()["node1"]` to get access
to a node object. This commit changes it to be more consistent with
dtest.
Use universalasync library to make test.py async code compatible
with synchronous code of dtest/ccm
Also, copied unmodified error_example_test.py from dtest as an example.
Run the test in `dev` mode only.