tests/qapi-schema: Rename tests from data- to args-

Since every schema entity has 'data', the data- prefix conveys no
information.  These tests actually exercise commands.  Only commands
have arguments, so change the prefix to to args-.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

tests/qapi-schema/args-array-empty.json

@@ -0,0 +1,2 @@
+# we reject an array for data if it does not contain a known type
+{ 'command': 'oops', 'data': { 'empty': [ ] } }