lttng: Do not rebuild the SS in every single state system test

lttng: Do not rebuild the SS in every single state system test

At some point we changed the state system tests to rebuild the whole
thing in the @Before, because at that point AssumeTrue() inside a
@BeforeClass did not work very well. Unfortunately this made running
the tests much longer.

Instead, really build the analysis/state system once per test class,
but only keep the AssumeTrue() in the main @Before that is ran every
test. That check will test a static boolean set by the @BeforeClass.

tl;dr Make the state system tests ~20 times faster.

Change-Id: I96a137e0d2ec871f92efe586ba6456aca0a61129
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/36184
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>