Set scenario.dhcp_client to dhcpcd by default

The reason is that python-tempestconf sets cirros >= 0.6.0 as the default
image and cirros version since 0.6.0 use dhcpcd as a default dhcp client.

Change-Id: I24023ad2b181b74397569ac7f81701218a8e2a2e

config_tempest/main.py

@@ -110,6 +110,12 @@ def load_basic_defaults(conf):
         ],
         "network-feature-enabled": [
             ("ipv6_subnet_attributes", "true")
+        ],
+        "scenario": [
+            # Since cirros version 0.6.0, dhcpcd dhcp client is the default
+            # and because tempestconf sets default cirros >= 0.6.0 by default,
+            # we can also set the dhcp client to dhcpcd by default
+            ("dhcp_client", "dhcpcd")
         ]}
 
     for section in default_values.keys():

doc/source/user/default.rst

@@ -43,3 +43,6 @@ Here is the list of tempest options, which are set by default:
     [network-feature-enabled]
     ipv6_subnet_attributes = true
 
+    [scenario]
+    dhcp_client = dhcpcd
+

releasenotes/notes/Set-dhcp_client-by-default-bf4e0705f2657803.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    From now on, python-tempestconf will set the following option by default
+
+    * ``CONF.scenario.dhcp_client dhcpcd``
+
+    The reason is that python-tempestconf sets cirros >= 0.6.0 as the default
+    image and cirros version since 0.6.0 use dhcpcd as a default dhcp client.
+