Switch to use goroutine profile in TestHttpsInsecure.

[aalexand]

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.

Tested:

$ cd internal/driver/
$ go test -c
$ taskset -c 0 stress -p 16 ./driver.test -test.v
17 runs so far, 0 failures
48 runs so far, 0 failures
76 runs so far, 0 failures
101 runs so far, 0 failures
128 runs so far, 0 failures
158 runs so far, 0 failures
184 runs so far, 0 failures
210 runs so far, 0 failures
239 runs so far, 0 failures
^C

Before the change the command would produce failing runs shortly after its start.

[codecov-io]

Codecov Report

Merging #350 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #350   +/-   ##
=======================================
  Coverage   66.52%   66.52%           
=======================================
  Files          36       36           
  Lines        7441     7441           
=======================================
  Hits         4950     4950           
  Misses       2087     2087           
  Partials      404      404

---

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