Convert generate-NOTICE.py to Python 3, fix name.

Python module names should be lower case and not use hyphens (the
former is a convention, the latter is a requirement for importable
modules).

Also updates the shell script to always use Python 3 so we don't need
to maintain Python 2 compatibility.

Test: repo upload, in both a python 2 and python 3 virtualenv
Bug: None
Change-Id: I486e54a12686b4e528dc6c9c47af5c7a52a7b790
diff --git a/tools/update_notice.sh b/tools/update_notice.sh
index a309bc2..302974f 100755
--- a/tools/update_notice.sh
+++ b/tools/update_notice.sh
@@ -1,7 +1,11 @@
 #!/bin/bash
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 cd $DIR/..
-./libc/tools/generate-NOTICE.py libc libm > libc/NOTICE
+python3 ./libc/tools/generate_notice.py libc libm > libc/NOTICE
+if [ $? -ne 0 ]; then
+  >&2 echo NOTICE file generation failed
+  exit 1
+fi
 
 git diff --exit-code HEAD libc/NOTICE
 exit $?