Enhance Integration test suite

[jandadav]

Integration test suite is major contributor to build time. Averaging around 7 minutes of runtime, it makes about 50%-80% of total build time.

I can see the following areas of improvement. Raising this issue to pin them down.

• [ ] REST calls optimizations: Use of RestAssured is inefficient. Expensive operations like opening connection or loading https context are repeated, causing below optimal performance. Leaking of RestAssured context between tests.
• [ ] DSL creation: standard things should be standardized. Faster and safer development of new tests.

[anton-brezina]

It would be very nice if we could actually measure how much we've improved and be able to report the improvement.

[achmelo]

split into: #1415 #1416 #1417

[balhar-jakub]

Will be managed in different issue.