Adding sudo to command _renew_lease_dhclient in remote_client

test_subnet_details failes because the command is missing sudo
Closes-Bug: 1435365

Change-Id: Ia7d403de194b493322a448aa0f771afacff56fd3
diff --git a/tempest/common/utils/linux/remote_client.py b/tempest/common/utils/linux/remote_client.py
index 1f1414f..b19faef 100644
--- a/tempest/common/utils/linux/remote_client.py
+++ b/tempest/common/utils/linux/remote_client.py
@@ -145,7 +145,7 @@
 
     def _renew_lease_dhclient(self, fixed_ip=None):
         """Renews DHCP lease via dhclient client. """
-        cmd = "sudo /sbin/dhclient -r && /sbin/dhclient"
+        cmd = "sudo /sbin/dhclient -r && sudo /sbin/dhclient"
         self.exec_command(cmd)
 
     def renew_lease(self, fixed_ip=None):