tmf: SWTBot integration tests for Project Explorer trace folders

tmf: SWTBot integration tests for Project Explorer trace folders

This covers 20 test scenarios from the test specification dealing
with trace folders, mostly dealing with importing traces. More test
will be added later to cover completely this section of the test
specification.

The change extracts some common code with existing tests.
Add more tests are added, we could remove some tests from the
non-integration test suite because there will be too much overlap.

Change-Id: I6d8e7753ca2341042a767a4a8e1f395041ff070b
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/79987
Reviewed-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>