Add a new "botbrowsertest" gulp-task, to allow running only the browser tests on the bots
Add a new "botbrowsertest" gulp-task, to allow running only the browser tests on the bots

Currently it's possible to run e.g. `gulp unittest`, `gulp fonttest`, and `gulp integrationtest` *separately* on the bots; see https://github.com/mozilla/botio-files-pdfjs
However, it's not possible to run *only* the `gulp browsertest` command on the bots without also running the full test-suite. In some cases, e.g. if the "browsertest" times out, having a way to only re-run those would thus save some time and resources.

If/when this patch lands, I'll follow-up with a patch adding a new `on_cmd_browsertest.js` file to the https://github.com/mozilla/botio-files-pdfjs repository.

timvandermeij/pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js,macroplant/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,nawawi/pdf.js,xavier114fch/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,timvandermeij/pdf.js,xavier114fch/pdf.js,Snuffleupagus/pdf.js,Snuffleupagus/pdf.js,macroplant/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,mozilla/pdf.js,nawawi/pdf.js,Shoobx/pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js