tests: print enum type members more like object type members

Commit 93bda4dd46 changed the internal representation of enum type
members from str to QAPISchemaMember, but we still print only a
string.  Has been good enough, as the name is the member's only
attribute of interest, but that's about to change.  To prepare, print
them more like object type members.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181213123724.4866-4-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

tests/qapi-schema/indented-expr.out

@@ -1,6 +1,13 @@
 object q_empty
-enum QType ['none', 'qnull', 'qnum', 'qstring', 'qdict', 'qlist', 'qbool']
+enum QType
     prefix QTYPE
+    member none
+    member qnull
+    member qnum
+    member qstring
+    member qdict
+    member qlist
+    member qbool
 module indented-expr.json
 command eins None -> None
    gen=True success_response=True boxed=False oob=False preconfig=False