Flaky tests

as seen in #64, some system test (often failing on SWTBot)
however, it would be better to understand why it fails and add the correct timing (or control in the actions themselves) at the right place rather that just retry automatically as suggested in #64

So this issue will try to trace facts and relevant messages in order to fix them at the source: (we keep the title of the issue geneiric as we don't know yet the real cause(s) as there might have several.

For example, looking at ://ci.eclipse.org/gemoc/job/gemoc-studio/job/move_dsl_default_lochttpation_to_project_root/ the build 6 an d 8 there is no commit.

let's try to identify the real cause:
current flaky tests in build 6: https://ci.eclipse.org/gemoc/job/gemoc-studio/job/move_dsl_default_location_to_project_root/6/
- org.eclipse.gemoc.studio.tests.system.mwb.userstory.DebugOfficialExampleK3FSM_Test.test01_TwoStatesUpCast_Model_some_steps_stop_and_clear
- org.eclipse.gemoc.studio.tests.system.mwb.userstory.DebugOfficialExampleK3FSM_Test.test02_secondRun_TwoStatesUpCast_Model_some_steps_stop_and_clear

- org.eclipse.gemoc.studio.tests.system.mwb.userstory.DeployOfficialExampleK3FSM_Test.test02_DebugPredefinedK3Fsm_TwoStatesUpCast_Model_some_steps_and_stop

all 3 seems related to the modeling workbench

One has a strange issue about java version incompatibility (https://ci.eclipse.org/gemoc/job/gemoc-studio/job/move_dsl_default_location_to_project_root/6/testReport/junit/org.eclipse.gemoc.studio.tests.system.mwb.userstory/DebugOfficialExampleK3FSM_Test/test01_TwoStatesUpCast_Model_some_steps_stop_and_clear/) (UnsupportedClassVersionError: org/eclipse/gemoc/addon/multidimensional/timeline/views/MultidimensionalTimelineViewPart has been compiled by a more recent version of the Java Runtime (class file version 54.0)

this is strange since the test will pass later ...

in build 7: only 2 remains https://ci.eclipse.org/gemoc/job/gemoc-studio/job/move_dsl_default_location_to_project_root/7/testReport/

and pass completly in build 8