Trying to test against /debug/pprof/profile has been giving some flakes
and trouble so far (#146, #253, #328, golang/go#24611, golang/go#22594). While
some of the discussions the failures triggered appear to be useful (such
as whether CPU profiles are expected to be working on Windows XP or
not), that kind of testing is not really in the scope for this
particular test. This change switches the test to use goroutine profile
instead which is hopefully much less dependent on the environment. The
change also makes the test much faster to run.