Bug 510678 - Cleanup o.e.test.performance.ui

* Add override annotations.
* Move away of new *Scope to *Scope.INSTANCE.
* Convert to lambdas.
* Use try-with-resources.
* Enable more warnings

Change-Id: I770e6f4d37de85ee80274b1abd4456ee392e3214
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>