Add support for suite level setup and teardown

[datakurre]

Currently robotsuite run each test case in isolation and also runs robot test suite setup and teardown individually for each test case.

[datakurre]

@tisto I was supposed to comment you about this issue today.

So, your wish was for a "real" support for robotframework suite level setups and teardowns so that we would not need to open Selenium test browser separately for each test case, but would keep the browser open for all tests in the same robotframework test suite. (zope.testrunner layer level browser would be even better, but unrealistic)

The main issue is that robotsuite passes the control of test execution from robotframework for zope.testrunner (or in theory some other Python unittest test runner). Robotsuite parses all tests from robotfamework test suite, passes them as individual tests for zope.testrunner and zope.testrunner runs them in order it wishes, making it hard and fragile to manage any state between tests.

For the fix, I'd suggest an environment variable controlled feature, which disables the feature described above and reports each robotframework test suite as a single unittest for zope.testrunner. The downside is that any failing test case would report the whole test suite as failing for zope.testrunner. But this might too bad, because we would still get full robotframework test report pointing the failing test case in the suite, and only difference seen with Jenkins is lower number of reported "unittests" (because of merged robotframework test cases).