Backport test improvements

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/django_gpg/tests/mixins.py

@@ -0,0 +1,10 @@
+from __future__ import unicode_literals
+
+from ..models import Key
+
+from .literals import TEST_KEY_DATA
+
+
+class KeyTestMixin(object):
+    def _create_test_key(self):
+        self.test_key = Key.objects.create(key_data=TEST_KEY_DATA)