Ldap bind-dn and bind-pwd are required even for non group authentication

[bhataprameya]

      - AUTH_TYPE=ldap
      - LDAP_METHOD=simple
      - LDAP_URL=ldap://ldap:389
      - LDAP_BASE_DN=DC=example,DC=org
      - LDAP_USER_TEMPLATE=uid=%s,%s

Just giving the above configs won't work because even if the base-dn and user-attr-template in LDAP group search config is always picked up from the parent level if not specified. (https://github.com/lmenezes/cerebro/blob/v0.9.4/app/controllers/auth/ldap/LDAPAuthConfig.scala#L24) (https://github.com/lmenezes/cerebro/blob/v0.9.4/app/controllers/auth/ldap/LDAPAuthConfig.scala#L26)

this causes the LDAP group search config to Nonempty causing line 63 to execute always instead of line 64.