Fixes currentRouteName middleware reporter test failures

[drewlee]

Fixes issue #489.

The recent release of @ember/test-helpers v2.9.0 added an assertion error that is emitted if the route name isn't available for a particular test. This results in a slew of unrelated application test failures when running the middleware reporter.

The resulting test failures typically consist of:

Promise rejected during "clicking the View Permissions button brings up the View modal": Assertion Failed: currentRouteName shoudl be a string"Source:
Error: Assertion Failed: currentRouteName shoudl be a string
    at assert (http://localhost:4444/talent/assets/vendor-static.js:32729:15)
    at currentRouteName (http://localhost:4444/talent/assets/test-support.js:22729:75)
    at middlewareReporter (http://localhost:4444/talent/assets/test-support.js:32566:61)
    at async http://localhost:4444/talent/assets/test-support.js:32499:11
    at async Promise.all (index 0)
    at async Object.<anonymous> (http://localhost:4444/talent/assets/tests.js:32489:7)"

The fix introduces a loose wrapper around the currentRouteName call, which absorbs the error, preventing it from getting emitted up to the test scope. All other behavior remains unchanged.

[scalvert]

Seems unfortunate that this breaking change caused such a downstream affect. Thanks for fixing!