runtime: make GC runtime stats test run on GCE

[bradfitz]

In https://code.google.com/p/go/source/detail?r=ec6629ef3dae19 I removed part of a test
that Dmitry liked because it doesn't run on GCE (which only has ~1ms timers apparently).

This bug is about restoring the test somehow. We could make it a -short test (so it's
skipped on builders, but runs on our machiens). Or try the test first and if we get a
0ns pause, then generate a lot of garbage and try for a >= 1 ms GC pause, which is
measurable on Windows (physical hardware) and GCE (any OS).

[griesemer]

Comment 1:

Labels changed: added repo-main.

[rsc]

There are 256 pause times in ms.PauseNs. The code could look at them to see if there is any sub-ms granularity, or anything < 1ms, before rejecting 0.

@dvyukov