cooker.py: Allow parsing shutdown to be called more than once

The parsing shutdown call can occur more than once. Currently
if this happens the code will hang. Add some code to prevent this.

[YOCTO #2039 partial]

(Bitbake rev: 7614c5bdcaf9d70614b4fad2ca02c7e6eaa92f1b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -1556,6 +1556,7 @@ class CookerParser(object):
         self.progress_chunk = max(self.toparse / 100, 1)
 
         self.start()
+        self.haveshutdown = False
 
     def start(self):
         self.results = self.load_cached()
@@ -1582,6 +1583,9 @@ class CookerParser(object):
     def shutdown(self, clean=True, force=False):
         if not self.toparse:
             return
+        if self.haveshutdown:
+            return
+        self.haveshutdown = True
 
         if clean:
             event = bb.event.ParseCompleted(self.cached, self.parsed,