* ci: make ember-ci-test (browserstack) VLTES-28

* Update .circleci/config.yml
Co-Authored-By: Josh Freda <jfreda@users.noreply.github.com>

* Update .circleci/config.yml
Co-Authored-By: Josh Freda <jfreda@users.noreply.github.com>

* ci: rename test-ember -> test-ui-browserstack

* Makefile: ember-ci-test -> test-ui-browserstack

- Use the same name for this test everywhere to reduce cognitive load.

* browserstack: exit non-zero on failure to connect

* .travis.yml: ember-ci-test -> test-ui-browserstack

* browserstack: add vault bin to the path

* Makefile: browserstack: fail early w/clear msgs

This might save someone time later. The same checks could be applied
elsewhere too trivially.