Fix manifest_fixer.py warnings

Fix a few warnings showing up in manifest_*.py

Test: manifest_fixer_test.py
Test: manifest_check_test.py
Flag: EXEMPT refactor
Change-Id: I144100d6d4aa7f5dff7eec79b4bd2d9d5da52153

scripts/manifest.py

@@ -25,7 +25,7 @@ android_ns = 'http://schemas.android.com/apk/res/android'
 
 def get_children_with_tag(parent, tag_name):
   children = []
-  for child in  parent.childNodes:
+  for child in parent.childNodes:
     if child.nodeType == minidom.Node.ELEMENT_NODE and \
        child.tagName == tag_name:
       children.append(child)