clases/lib: Use modern exception syntax

Update older code to use modern exception handling syntax which
is the form accepted by python 3.

(From OE-Core rev: b010501cd089e649a68f683be0cf4d0aac90fbe3)

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

meta/lib/oe/utils.py

@@ -1,7 +1,7 @@
 def read_file(filename):
     try:
         f = file( filename, "r" )
-    except IOError, reason:
+    except IOError as reason:
         return "" # WARNING: can't raise an error now because of the new RDEPENDS handling. This is a bit ugly. :M:
     else:
         return f.read().strip()