ONOS-6524: Added Code Coverage tools to gulp

When `gulp test` is executed, Karma will now generate an interactive html report for code coverage in each file. The folder can be found in web/gui/src/main/webapp/tests/coverage

Change-Id: I951ac1bea7f3f0ca35deb9cc823bb883bcd9f8a5
diff --git a/.gitignore b/.gitignore
index 307c56c..f7bbf70 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,6 +28,7 @@
 web/gui/src/main/webapp/tests/node_modules
 web/gui/src/test/_karma/node_modules
 web/gui/src/main/webapp/node_modules/
+web/gui/src/main/webapp/tests/coverage
 web/gui/src/main/webapp/dist/
 
 npm-debug.log