fix: Removing store validity tests from stress.py (#3170)

Store validity checks are executed on each `get_status` and take up to 1.5 seconds, during which they block `Client`.
In stress.py specifically they quickly get to actually taking 1.5 seconds, thus each time the test calls to `get_status`, one of the nodes gets blocked for 1.5s.

Removing ongoing store validity checks from stress.py, and introducing them only once at the end.

Test plan:
----------
stress.py now can actually pass in nayduck:
http://nayduck.eastus.cloudapp.azure.com:3000/#/run/93

The failure is a new issue: #3169

pytest/tests/stress/stress.py

@@ -561,12 +561,14 @@ def doit(s, n, N, k, monkeys, timeout):
     started = time.time()
 
     boot_node = spin_up_node(config, near_root, node_dirs[0], 0, None, None)
+    boot_node.stop_checking_store()
     boot_node.mess_with = False
     nodes = [boot_node]
 
     for i in range(1, N + k + 1):
         node = spin_up_node(config, near_root, node_dirs[i], i,
                             boot_node.node_key.pk, boot_node.addr())
+        node.stop_checking_store()
         nodes.append(node)
         if i >= n and i < N:
             node.kill()
@@ -641,6 +643,11 @@ def check_errors():
 
     check_errors()
 
+    logging.info("Shut down complete, executing store validity checks")
+    for node in nodes:
+        node.is_check_store = True
+        node.check_store()
+
 
 MONKEYS = dict([(name[7:], obj)
                 for name, obj in inspect.getmembers(sys.modules[__name__])