Don't bother with persistent connections when testing NURLs.

src/allmydata/storage/http_client.py

@@ -311,18 +311,20 @@ class StorageClient(object):
 
     @classmethod
     def from_nurl(
-        cls,
-        nurl: DecodedURL,
-        reactor,
+        cls, nurl: DecodedURL, reactor, persistent=True, retryAutomatically=True
     ) -> StorageClient:
         """
         Create a ``StorageClient`` for the given NURL.
+
+        ``persistent`` and ``retryAutomatically`` arguments are passed to the
+        new HTTPConnectionPool.
         """
         assert nurl.fragment == "v=1"
         assert nurl.scheme == "pb"
         swissnum = nurl.path[0].encode("ascii")
         certificate_hash = nurl.user.encode("ascii")
-        pool = HTTPConnectionPool(reactor)
+        pool = HTTPConnectionPool(reactor, persistent=persistent)
+        pool.retryAutomatically = retryAutomatically
         pool.maxPersistentPerHost = 20
 
         if cls.TEST_MODE_REGISTER_HTTP_POOL is not None:

src/allmydata/storage_client.py

@@ -1203,8 +1203,12 @@ class HTTPNativeStorageServer(service.MultiService):
             # the HTTP server to talk to, we don't have connection status
             # updates... https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3978
             def request(reactor, nurl: DecodedURL):
+                # Since we're just using this one off to check if the NURL
+                # works, no need for persistent pool or other fanciness.
                 return StorageClientGeneral(
-                    StorageClient.from_nurl(nurl, reactor)
+                    StorageClient.from_nurl(
+                        nurl, reactor, persistent=False, retryAutomatically=False
+                    )
                 ).get_version()
 
             # LoopingCall.stop() doesn't cancel Deferreds, unfortunately: