Allow json response plugin to be suppressed

Add a static class member suppress_json_resp that when
set to True will prevent the JsonApiResp plugin from
responding with a json wrapper.

Change-Id: I43aadb6b59bb21ef53e5252e4878157c8e13935e
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/module/obmc/wsgi/apps/rest_dbus.py b/module/obmc/wsgi/apps/rest_dbus.py
index 43d1f03..8cbbabc 100644
--- a/module/obmc/wsgi/apps/rest_dbus.py
+++ b/module/obmc/wsgi/apps/rest_dbus.py
@@ -713,6 +713,7 @@
     content_type = 'application/octet-stream'
     ''' TODO openbmc/issues #1795, Change dump path'''
     dump_loc = '/tmp/dumps'
+    suppress_json_resp = True
 
     def __init__(self, app, bus):
         super(DownloadDumpHandler, self).__init__(
@@ -934,9 +935,9 @@
         app.install_error_callback(self.error_callback)
 
     def apply(self, callback, route):
-        content_type = getattr(
-            route.get_undecorated_callback(), '_content_type', None)
-        if self.json_type != content_type:
+        skip = getattr(
+            route.get_undecorated_callback(), 'suppress_json_resp', None)
+        if skip:
             return callback
 
         def wrap(*a, **kw):