Don't check for thread running in terminateLoopSoon()

Don't check for thread running in terminateLoopSoon()

Summary:
Consider this use case:
thread 1:
make an evb
create and start thread 2
do some work
evb->terminateLoopSoon()
join thread 2 with a timeout
thread 2:
do some initialization
evb->loop()
Normally, this all works fine.  However, if the work thread 1 has to do is sufficiently small, and no external input occurs (one of the thing the evb is doing is listening on a socket), then sometimes, terminateLoopSoon() happens before loop() is called (or at least, before loopThread_.store() happens). isRunning() in terminateLoopSoon() is false, and so stop_ is never set, and event_base_loopbreak() is never called. The join times out, and thread 2 is still running.  Removing the isRunning() check gives the desired behavior.

Test Plan:
In my ad hoc tests, this fix caused my threads to exit when
I wanted them to exit in a situation like the one above.

Reviewed By: andrewcox@fb.com

FB internal diff: D1455885

Tasks: 2057547