burnin: Fix a bug in ImagesTestCase

Filter images list so it does not contain burnin's registered
images. This way we reduce the posibility that images list and
detailed images list have different number of images.

snf-tools/synnefo_tools/burnin.py

@@ -236,8 +236,12 @@ class ImagesTestCase(unittest.TestCase):
         log.info("Getting simple and detailed list of images")
         cls.client = ComputeClient(API, TOKEN)
         cls.plankton = ImageClient(PLANKTON, TOKEN)
-        cls.images = cls.plankton.list_public()
-        cls.dimages = cls.plankton.list_public(detail=True)
+        cls.images = \
+            filter(lambda x: not x['name'].startswith(SNF_TEST_PREFIX),
+                   cls.plankton.list_public())
+        cls.dimages = \
+            filter(lambda x: not x['name'].startswith(SNF_TEST_PREFIX),
+                   cls.plankton.list_public(detail=True))
         cls.result_dict = dict()
         # Get uniq user id
         cls.uuid = _get_user_id()