Add support for dhcpcd in the renew_lease method

In Cirros 0.6.0 and newer there is dhcpcd client used instead of old
udhcpc. This patch adds support to that new client in the
remote_client's renew_lease method.

Related-Bug: #2003063
Change-Id: I5d5648332e1c84221e708c29a904fcaaffdb451e
diff --git a/tempest/config.py b/tempest/config.py
index d91fca4..f1eb647 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -1203,10 +1203,10 @@
     # TODO(yfried): add support for dhcpcd
     cfg.StrOpt('dhcp_client',
                default='udhcpc',
-               choices=["udhcpc", "dhclient", ""],
+               choices=["udhcpc", "dhclient", "dhcpcd", ""],
                help='DHCP client used by images to renew DCHP lease. '
                     'If left empty, update operation will be skipped. '
-                    'Supported clients: "udhcpc", "dhclient"'),
+                    'Supported clients: "udhcpc", "dhclient", "dhcpcd"'),
     cfg.StrOpt('protocol',
                default='icmp',
                choices=('icmp', 'tcp', 'udp'),