Fix import of Router module

Since the router.js sync in cf0caa04f625067ec3b4629acdec12c8517df94e,
the Router is now stored in the "default" property.
Add spec for unhandled exception being logged by Test.adapter.exception

The changes in exception handling introduced in
cf0caa04f625067ec3b4629acdec12c8517df94e made a test assertion in an
existing test obsolete, since it wasn't called anymore.

This commit adds a spec for Test.adapter.exception being invoked, when
an exception is not handled.