Clean up exception handling in TestON core

    - Catch more specific exceptions
    - Clearer Style
    - Allow CTRL-C to exit the test cleanly whether from the TestON
      cli or ruinning as a script

Change-Id: I7f2e8eeba5229f97c87e06b49a585933a61fa4ad
diff --git a/TestON/core/xmldict.py b/TestON/core/xmldict.py
index 2cc47da..8d1dcf4 100644
--- a/TestON/core/xmldict.py
+++ b/TestON/core/xmldict.py
@@ -37,7 +37,7 @@
         root = ElementTree.XML(root_or_str)
     try :
         return {root.tag: _from_xml(root, strict)}
-    except Exception:
+    except StandardError:
         return None
 
 def dict_to_xml(dict_xml):