doc: Capitalize keystone domain name

There is an inconsistency for keystone domain names
in the nova doc. ('default' and 'Default')
Replace 'default' with 'Default'.

Change-Id: I437092d04b0cbea78942efd5f565734f34bcbcb2
Closes-Bug: #1821411

doc/source/install/compute-install-obs.rst

@@ -77,8 +77,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS

doc/source/install/compute-install-rdo.rst

@@ -69,8 +69,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS

doc/source/install/compute-install-ubuntu.rst

@@ -59,8 +59,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS

doc/source/install/controller-install-obs.rst

@@ -243,8 +243,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS

doc/source/install/controller-install-rdo.rst

@@ -226,8 +226,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS

doc/source/install/controller-install-ubuntu.rst

@@ -224,8 +224,8 @@ Install and configure components
         auth_url = http://controller:5000/v3
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = nova
         password = NOVA_PASS