Handle multiple LDAP users more gracefully

[derek63]

Right now, the login module will force an error if more than one LDAP user matches the query generated from the certificate principal (uid=my-principal). See

https://github.com/lightblue-platform/lightblue-rest/blob/master/auth/src/main/java/com/redhat/lightblue/rest/auth/ldap/CachedLdapFindUserRolesByUidCommand.java#L89

While this is certainly one way to handle it, a better way would be to merge all of the permissions for any of the DNs, as there definitely could be multiple matching ids somewhere in LDAP