fix archive files being created with perms 000

In python 2.5 and earlier, ZipFile.writestr(filename, data) results in
the file being added to the archive with permissions 000.  (See
http://svn.python.org/view?view=rev&revision=65235.)  Work around this
by creating a ZipInfo object and setting the permissions explicitly.
diff --git a/tools/releasetools/sign_target_files_apks b/tools/releasetools/sign_target_files_apks
index 9f393c8..bc04956 100755
--- a/tools/releasetools/sign_target_files_apks
+++ b/tools/releasetools/sign_target_files_apks
@@ -283,7 +283,7 @@
   data, _ = p.communicate()
   if p.returncode != 0:
     raise ExternalError("failed to run dumpkeys")
-  output_tf_zip.writestr("RECOVERY/RAMDISK/res/keys", data)
+  common.ZipWriteStr(output_tf_zip, "RECOVERY/RAMDISK/res/keys", data)
 
   # SystemUpdateActivity uses the x509.pem version of the keys, but
   # put into a zipfile system/etc/security/otacerts.zip.
@@ -293,8 +293,8 @@
   for k in mapped_keys:
     certs_zip.write(k)
   certs_zip.close()
-  output_tf_zip.writestr("SYSTEM/etc/security/otacerts.zip",
-                         tempfile.getvalue())
+  common.ZipWriteStr(output_tf_zip, "SYSTEM/etc/security/otacerts.zip",
+                     tempfile.getvalue())
 
 
 def main(argv):