Test for error in setUpClass

New test environment (new fixture data in nailgun_mimic.py, new fake
test for produce given error was added to dummy_tests, new test in
functional tests to test errorness behaviour) was added.

Fix bug with updating tests status after unhandled exception in
setUpClass of test case.

Method _add_message of StoragePlugin class from nose_storage_plugin.py
has been modified so that it now updates tests for ContextSuite with
error properly. New util function get_tests_ids_to_update was added to
nose_utils.py. This function performs recursive searching of tests in
ContextSuite object. Such functionality takes is needed in orded to
avoid problems that may occur when uhandled exception is raised in
setUpClass method of TestCase. Functional tests for new behaviour have
been created. Some non-major fixes and refactoring of different chunks
were added.

Change-Id: I5ef9cd7a139425ae38ac54a396301b7d0763b4d2