Ticket 486 - nsslapd-enablePlugin should not be multivalued
Bug Description: Certain core DS schema attributes are defined multivalued, but some should be single valued.
Fix Description: Went through all the plugin, snmp, and replication attributes, and correctly set which
ones should be single valued.
Reviewed by: richm(Thanks!)
(cherry picked from commit 70117a15bf70259ec978fd696cb0da08faf2cc29)