bitbake: tinfoil: add context manager functions

Since calling the shutdown() function is highly recommended, make
tinfoil objects a little easier to deal with by adding context manager
support - so you can do the following:

    with bb.tinfoil.Tinfoil() as tinfoil:
        tinfoil.prepare(True)
        ...

(Bitbake rev: f59bc6be2b4af1acdcf6a1b184956b5ffd297743)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/tinfoil.py

@@ -59,6 +59,12 @@ class Tinfoil:
     def register_idle_function(self, function, data):
         pass
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.shutdown()
+
     def parseRecipes(self):
         sys.stderr.write("Parsing recipes..")
         self.logger.setLevel(logging.WARNING)