Change the .gitignore pattern for plugins from a blacklist to a whitelist

Change-Id: Ibda4cd9281f79667c9fbdd1e58760ae163b2779a
diff --git a/.gitignore b/.gitignore
index 8cd43dd..c0e14ab 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,6 +32,18 @@
 /local.properties
 /node_modules/
 /package-lock.json
-/plugins/cookbook-plugin/
+/plugins/*
+!/plugins/BUILD
+!/plugins/codemirror-editor
+!/plugins/commit-message-length-validator
+!/plugins/delete-project
+!/plugins/download-commands
+!/plugins/external_plugin_deps.bzl
+!/plugins/gitiles
+!/plugins/hooks
+!/plugins/replication
+!/plugins/reviewnotes
+!/plugins/singleusergroup
+!/plugins/webhooks
 /test_site
 /tools/format