details: Add OS name view/edit, + oslist rework

This is just a big nasty commit.

Turn the OS inspection page into an always available page that
shows the libosinfo name from the domain metadata XML. Use oslist.py
and have it absorb more of the common behavior needed by create.py
and details.py. Add UI tests for it all

tests/xmlparse.py

@@ -116,7 +116,10 @@ class XMLParseTest(unittest.TestCase):
         check("on_lockfailure", "poweroff", "restart")
 
         check = self._make_checker(guest._metadata.libosinfo)  # pylint: disable=protected-access
-        check("os_id", "http://fedoraproject.org/fedora/17", "frib")
+        check("os_id", "http://fedoraproject.org/fedora/17")
+        guest.set_os_name("generic")
+        check("os_id", None, "frib")
+        self.assertEqual(guest.osinfo.name, "generic")
 
         check = self._make_checker(guest.clock)
         check("offset", "utc", "localtime")