Matching bu `apiName@wallTime` fails when two actions start at the same
time, e.g. two parallel api requests. Moreover, it results in trace
actions that have parent set to themselves, which in turn causes
infinite loop in the trace viewer. To avoid this problems we write
stepId explicitly to the library trace and use those step ids to find
corresponding test runner steps.
The stepId is passed via zone in case of expect, because the protocol
step is quite deep in the call chain after or explicitly in case of API
call steps created by the test runner instrumentation.
