Use designated test domains (RFC2606) in tests

Some tests were using domain names that were intended to be "fake", but are
actually registered domain names (such as mycorp.com).

Even though we were not actually making connections to these domains, it's
better to use domains that are designated for testing/examples in RFC2606:
https://tools.ietf.org/html/rfc2606

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/context/testdata/inspect.golden

@@ -7,11 +7,11 @@
         },
         "Endpoints": {
             "docker": {
-                "Host": "https://someswarmserver",
+                "Host": "https://someswarmserver.example.com",
                 "SkipTLSVerify": false
             },
             "kubernetes": {
-                "Host": "https://someserver",
+                "Host": "https://someserver.example.com",
                 "SkipTLSVerify": false,
                 "DefaultNamespace": "default"
             }

cli/command/context/testdata/list.golden

@@ -1,5 +1,5 @@
-NAME        DESCRIPTION                               DOCKER ENDPOINT               KUBERNETES ENDPOINT            ORCHESTRATOR
-current *   description of current                    https://someswarmserver       https://someserver (default)   all
-default     Current DOCKER_HOST based configuration   unix:///var/run/docker.sock                                  swarm
-other       description of other                      https://someswarmserver       https://someserver (default)   all
-unset       description of unset                      https://someswarmserver       https://someserver (default)   
+NAME        DESCRIPTION                               DOCKER ENDPOINT                       KUBERNETES ENDPOINT                        ORCHESTRATOR
+current *   description of current                    https://someswarmserver.example.com   https://someserver.example.com (default)   all
+default     Current DOCKER_HOST based configuration   unix:///var/run/docker.sock                                                      swarm
+other       description of other                      https://someswarmserver.example.com   https://someserver.example.com (default)   all
+unset       description of unset                      https://someswarmserver.example.com   https://someserver.example.com (default)   

cli/command/context/testdata/test-kubeconfig

@@ -2,7 +2,7 @@ apiVersion: v1
 clusters:
 - cluster:
     certificate-authority-data: dGhlLWNh
-    server: https://someserver
+    server: https://someserver.example.com
   name: test-cluster
 contexts:
 - context: