Do not skip test_user_enable_attribute_mask in _ldap_livetest

This test is usable with OpenLDAP and is useful for validation.

Change-Id: Ie4da746a17d2ca545eb1125c1e7249620f0efbc0
Related-Bug: #1210175
Fix test_user_enable_attribute_mask so it actually tests

test_user_enable_attribute_mask wasn't actually testing
user_enable_attribute_mask because it didn't reload the backend
after changing the config value.

Change-Id: I9fa6bebe0c4b3d2afc1eb53867cf217b046b0210
Related-Bug: #1210175