Fix test failure in updater when adding values to a single-value attr

The ipaldap.py code was updated to consider the schema when making
changes and does a REPLACE on single-value attributes. So when you
do an add in an update it will effectively replace the value instead
of ignoring it.

tests/test_install/4_update.update

@@ -1,3 +1,4 @@
+# Replace the existing SINGLE-VALUE gecos with a new value thru add
 dn: uid=tuser, cn=test, cn=accounts, $SUFFIX
 add:gecos: Test User New2
 

tests/test_install/test_updates.py

@@ -126,7 +126,7 @@ class test_update(object):
         Test the updater adding a new value to a single-valued attribute
         """
         modified = self.updater.update([self.testdir + "4_update.update"])
-        assert(modified == False)
+        assert(modified == True)
 
     def test_5_update(self):
         """