qapi-visit: Honor prefix of discriminator enum

When we added support for a user-specified prefix for an enum
type (commit 351d36e), we forgot to teach the qapi-visit code
to honor that prefix in the case of using a prefixed enum as
the discriminator for a flat union.  While there is still some
on-list debate on whether we want to keep prefixes, we should
at least make it work as long as it is still part of the code
base.

Reported-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1455665965-27638-1-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index 4b89527..353a34e 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -73,14 +73,17 @@
   'base': 'UserDefZero',
   'data': { 'string': 'str', 'enum1': 'EnumOne' } }
 
+{ 'struct': 'UserDefUnionBase2',
+  'base': 'UserDefZero',
+  'data': { 'string': 'str', 'enum1': 'QEnumTwo' } }
+
 # this variant of UserDefFlatUnion defaults to a union that uses fields with
 # allocated types to test corner cases in the cleanup/dealloc visitor
 { 'union': 'UserDefFlatUnion2',
-  'base': 'UserDefUnionBase',
+  'base': 'UserDefUnionBase2',
   'discriminator': 'enum1',
   'data': { 'value1' : 'UserDefC', # intentional forward reference
-            'value2' : 'UserDefB',
-            'value3' : 'UserDefA' } }
+            'value2' : 'UserDefB' } }
 
 { 'alternate': 'UserDefAlternate',
   'data': { 'uda': 'UserDefA', 's': 'str', 'i': 'int' } }