Fix issue with bad dns zookeeper test

* I think this test was passing by luck because we didn't have any real
  operations that interacted with that cell. Given the global topology refactor
  part of this PR, this has changed and now this breaks.
* I think the regression happened when samuel/go-zookeeper was introduced, but
  this was never discovered. This test was originally introduced in:
  c685aaf243

Signed-off-by: Rafael Chacon <rafael@slack-corp.com>

go/vt/topo/shard.go

@@ -512,7 +512,7 @@ func (ts *Server) FindAllTabletAliasesInShardByCell(ctx context.Context, keyspac
 	ctx = trace.NewContext(ctx, span)
 	var err error
 
-	// The caller intents to update all cells in this case
+	// The caller intents to all cells
 	if len(cells) == 0 {
 		cells, err = ts.GetCellInfoNames(ctx)
 		if err != nil {

test/tabletmanager.py

@@ -46,12 +46,7 @@ healthy_expr = re.compile(r'Current status: <span.+?>healthy')
 def setUpModule():
   try:
     topo_flavor = environment.topo_server().flavor()
-    if topo_flavor == 'zk2':
-      # This is a one-off test to make sure our 'zk2' implementation
-      # behave with a server that is not DNS-resolveable.
-      environment.topo_server().setup(add_bad_host=True)
-    else:
-      environment.topo_server().setup()
+    environment.topo_server().setup()
 
     # start mysql instance external to the test
     setup_procs = [

test/tabletmanager2.py

@@ -56,12 +56,7 @@ class TestServiceTestOfTabletManager(unittest.TestCase):
 
         try:
             topo_flavor = environment.topo_server().flavor()
-            if topo_flavor == 'zk2':
-                # This is a one-off test to make sure our 'zk2' implementation
-                # behave with a server that is not DNS-resolveable.
-                environment.topo_server().setup(add_bad_host=True)
-            else:
-                environment.topo_server().setup()
+            environment.topo_server().setup()
 
             # start mysql instance external to the test
             setup_procs = [

test/topo_flavor/zk2.py

@@ -40,7 +40,7 @@ class Zk2TopoServer(server.TopoServer):
     self.addr = 'localhost:%d' % (self.zk_port_base + 2)
     self.ports_assigned = True
 
-  def setup(self, add_bad_host=False):
+  def setup(self):
     from environment import run, binary_args, vtlogroot  # pylint: disable=g-import-not-at-top,g-multiple-import
     import utils  # pylint: disable=g-import-not-at-top
 
@@ -60,8 +60,6 @@ class Zk2TopoServer(server.TopoServer):
                            '-server_address', self.addr,
                            'test_ny'])
     ca_addr = self.addr
-    if add_bad_host:
-      ca_addr += ',does.not.exists:1234'
     # Use UpdateCellInfo for this one, more coverage.
     utils.run_vtctl_vtctl(['UpdateCellInfo',
                            '-root', '/test_ca',