make it impossible to lie about the feature an output belongs to

overriding an output's 'feature' field would just lead to confusing
error messages. the right way is setting the 'name' field.

adjust the 'dbus' library output to this policy.

Change-Id: I912133f3a0a50fc55f2e16a1ed6bfa464aae8d88
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

configure.json

@@ -1788,7 +1788,7 @@
             "condition": "features.dbus && tests.dbus",
             "output": [
                 "publicQtConfig",
-                { "type": "library", "feature": "dbus", "test": "dbus" }
+                { "type": "library", "name": "dbus", "test": "dbus" }
             ]
         },
         "host-dbus": {

mkspecs/features/qt_configure.prf

@@ -1134,15 +1134,13 @@ defineTest(qtConfProcessOneOutput) {
     !defined("qtConfOutput_$$call", test): \
         error("Undefined type '$$call' in output '$$2' of feature '$$feature'.")
 
-    isEmpty($${opfx}.feature): \
-        $${opfx}.feature = $$feature
-
     condition = $$eval($${opfx}.condition)
     !isEmpty(condition) {
         !$$qtConfEvaluate($$condition): \
             return(false)
     }
 
+    $${opfx}.feature = $$feature
     qtConfOutput_$${call}($$opfx, $$eval($${fpfx}.available))
 }