runtime: restore "goroutine in C code" message

In the 1.9 upgrade I took out the word "goroutine" from a traceback
showing a goroutine running in C code, to let TestCgoNumGoroutine
pass.  However, it turns out that some code is actually checking for
that string; for example,
https://github.com/grpc/grpc-go/blob/master/test/leakcheck/leakcheck.go#L44
So keep the message the same, and change the test.

Change-Id: I69aff11970313599fa05f4e2e15f0de87660dcca
Reviewed-on: https://go-review.googlesource.com/64850
Reviewed-by: Than McIntosh <thanm@google.com>
2 files changed