Fix the broken signing script

check_target_files_signatures.py was accidentally broken due to the
renaming of a variable in last commit. It escaped the checking from
pylint because it was a keyword ('all').

Bug: 21611858
Change-Id: I58c983e59c4a3e0018481d3c9ba328ed76f5c08a

tools/releasetools/check_target_files_signatures.py

@@ -331,7 +331,7 @@ class TargetFiles(object):
 
     by_certpair = {}
 
-    for i in all:
+    for i in all_apks:
       if i in self.apks:
         if i in other.apks:
           # in both; should have same set of certs