bitbake: cooker: do not abort on single ctrl-c

After b7ed7e9a815c4e10447fd499508be3dbb47f06e8 bitbake aborts immediately
when a single ctrl-c is pressed.

Patch restores the previous behavior where a single ctrl-c waits for
active tasks to finish.

https://bugzilla.yoctoproject.org/show_bug.cgi?id=15094

(Bitbake rev: 66131fa6a3e12c28710d09e1dbf3c03f2981280d)

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -1764,9 +1764,9 @@ class BBCooker:
     def shutdown(self, force=False):
         if force:
             self.state = state.forceshutdown
+            bb.event._should_exit.set()
         else:
             self.state = state.shutdown
-        bb.event._should_exit.set()
 
         if self.parser:
             self.parser.shutdown(clean=False)