qa: add a log in case that a mysterious bug happens again

The bug is likely to be in the test rather than in NEO.

neo/tests/threaded/test.py

@@ -1704,7 +1704,18 @@ class Test(NEOThreadedTest):
                     x.value += 1
                     c2.root()['x'].value += 2
                     TransactionalResource(t1, 1, tpc_begin=begin1)
-                    s1m, = s1.getConnectionList(cluster.master)
+                    # BUG: Very rarely, getConnectionList returns more that 1
+                    #      connection ("too many values to unpack"), which is
+                    #       a mystery and impossible to reproduce:
+                    #      - 1st time: v1.8.1 on a test machine (no SSL)
+                    #      - last: current revision on my laptop (SSL),
+                    #              at the first iteration of this loop
+                    _sm = list(s1.getConnectionList(cluster.master))
+                    try:
+                        s1m, = _sm
+                    except ValueError:
+                        self.fail((_sm, list(
+                            s1.getConnectionList(cluster.master))))
                     try:
                         s1.em.removeReader(s1m)
                         with ConnectionFilter() as f, \