testing/testcase: include partition dump when setup class fail

Sometimes instanciation fail because some service do not start and the
"check port listening" promises fail. In this case, it's very important
to also have the partition content to see what's in the log files.

/reviewed-on nexedi/slapos.core!175

slapos/testing/testcase.py

@@ -434,7 +434,7 @@ class SlapOSInstanceTestCase(unittest.TestCase):
 
   @classmethod
   def _storeSystemSnapshot(cls, name):
-    """Store a snapshot of standalone slapos
+    """Store a snapshot of standalone slapos and partitions.
 
     Does not include software log, because this is stored at the end of software
     installation and software log is large.
@@ -450,6 +450,7 @@ class SlapOSInstanceTestCase(unittest.TestCase):
         cls._copySnapshot(standalone_log, name)
     # store slapproxy database
     cls._copySnapshot(cls.slap._proxy_database, name)
+    cls._storePartitionSnapshot(name)
 
   def tearDown(self):
     self._storePartitionSnapshot(self.id())