runtime/race: add a short test that runs in run.bash

[dvyukov]

Currently run.bash only tests:
go test -race -short flag
but this does not produce any race reports, so that code path is not tested.
Add a short test that produces a race report and is executed in run.bash.

[dvyukov]

Comment 1:

Owner changed to @dvyukov.

[dvyukov]

Comment 2:

This issue was closed by revision 2791ef0.

Status changed to Fixed.