Check for text in num_string_test

COUCHDB-2787
diff --git a/test/06-basic-text-test.py b/test/06-basic-text-test.py
index 493befc..28c495a 100644
--- a/test/06-basic-text-test.py
+++ b/test/06-basic-text-test.py
@@ -564,7 +564,8 @@
     def setUpClass(klass):
         super(NumStringTests, klass).setUpClass()
         klass.db.recreate()
-        klass.db.create_text_index()
+        if mango.has_text_service():
+            klass.db.create_text_index()
 
     # not available for python 2.7.x
     def isFinite(num):