lttng.swtbot: add state system explorer SWTBot test

lttng.swtbot: add state system explorer SWTBot test

This test runs three passes, opens the view, re-opens the view
then re-opens the trace.

Future tests can look at the content of the state system. This
test enumerates the state systems available.

Change-Id: I3136bb4bfc802d958d63981d7ca358f44248f0be
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/84711
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Hudson CI