Display layout plugin test coverage to 20% or more (#3158)

* Display layout plugin test coverage to 20% or more
Resolves #3157

* Changes address original issue? Yes
* Unit tests included and/or updated with changes? Yes
* Command line build passes? Yes
* Changes have been smoke-tested? Yes
* Testing instructions included? Yes

* Add disable-dev-shm-usage flag to ChromeHeadless launcher config in karma

* Adding disable dev shm usage flag to chromeheadless launcher and setting log level to debug

* Adding np activity timeout to 60000

* Adding no-sandbox flag for headless chrome

* Run tests without headless chrome to see if that fixes the fonts issue

* Fix typo

* Trying chrome headless with increased memory

* Reset karma.conf back to master

* Trying karma chrome launcher 3.1.0

* Revert to master code for package.json and karma.conf.js

* Trying node 12 browsers

* Revert back to node:13 browsers

* Revert to 10.2.1-browsers circle ci node browsers variant image for docker

* Rebuild node-sass for node 10.x

* Upgrading to 13.14.0 node

* Remove node options

* Don't restore cache before npm install

* Comment out tests with setTimeout

* Trying node 8-browsers

* Try firefox headless

* Firefox version typo

* Revert focused tests

* Exclude setTimeout tests

* Increase browser connectivity timeout

* Trying large timeout with Chromeheadless

* Going back to Firefox and setting browser timeout to 1.5 mins

* Fixes linting issues

* Fix broken tests and add some null checks in the code

* Change double quotes to single quotes

src/plugins/displayLayout/DisplayLayoutToolbar.js

@@ -550,7 +550,11 @@ define(['lodash'], function (_) {
                 function unitsOnly(items) {
                     let results = items.filter((item) => {
                         let currentItem = item[0];
-                        let metadata = this.openmct.telemetry.getMetadata(currentItem.context.item);
+                        let metadata = openmct.telemetry.getMetadata(currentItem.context.item);
+                        if (!metadata) {
+                            return false;
+                        }
+
                         let hasUnits = metadata
                             .valueMetadatas
                             .filter((metadatum) => metadatum.unit)