[pushed] Improve gdb.threads/attach-many-short-lived-threads.exp timeout handling

[Doug Evans]

On Fri, Feb 6, 2015 at 4:25 AM, Pedro Alves <palves@redhat.com> wrote:
> The buildbot shows that this test is still racy, and occasionally
> fails with time outs on some machines.  I'd like to get major issues
> with load out of the way.

Thanks for fixing this.

btw, how often do you run the testsuite in parallel?
I see such load related issues all the time that way.
[e.g., checkpoint.exp, gdb-sigterm.exp, et.al.]