Use multiple globs/emails in per-file syntax

Bug: 112259427
Test: tools/checkowners.py -c -v OWNERS */OWNERS */*/OWNERS
Change-Id: I0e2c2c64a23df360fbe7691c4336ca04099fba13
diff --git a/tools/OWNERS b/tools/OWNERS
index 7a23adc..7d666f1 100644
--- a/tools/OWNERS
+++ b/tools/OWNERS
@@ -1,2 +1 @@
-per-file warn.py = chh@google.com
-per-file checkowners.py = chh@google.com
+per-file warn.py,checkowners.py = chh@google.com