Fixups for threads_count usage and logging

In the cases where threads_count is not applicable (when a
custom executor is provided) we should not log a message that
says the number of threads being used (since it will likely
not be an accurate message of what the provided executor is
really using).

Change-Id: I092c69716f300b3ac95cc320c96243966eb982ba
Merge "Fixups for threads_count usage and logging"