Support for external SUDO users and hosts.

The SUDO details page has been modified to support external users
and hosts. In the backend, the internal and external users are kept
in separate attributes, but in the UI they will be displayed as a
single list. The same thing is done for hosts.

The ipa_sudorule_association_adder_dialog() has been modified such
that it only displays the external field if there is an external
attribute for that field.

install/static/test/data/sudorule_show.json

@@ -32,6 +32,12 @@
                 "test"
             ],
             "dn": "ipauniqueid=4fc57a02-f23311df-b268e50e-a3b3ef71,cn=sudorules,dc=dev,dc=example,dc=com",
+            "externalhost": [
+                "external.example.com"
+            ],
+            "externaluser": [
+                "external"
+            ],
             "ipasudorunas_user": [
                 "admin"
             ],