oeqa/core/decorator/oetimeout: Add support for OEQA threaded mode

oeqa/core/decorator/oetimeout: Add support for OEQA threaded mode

In python signals are only allowed to delivery into the main thread,
to support the threading mode test if the runner is threaded and
use threading.Timer instead.

There are some considerations like SIGALRM interrupts the execution
after N seconds but the Timer only starts a Thread to notice the
timeout and the exception will be raised when the test run ends.

[YOCTO #11450]

(From OE-Core rev: 8ab201612e22493dc2509ba339a8f07ade611a54)

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>