Singel node with partially deleted cluster configs won't start up

[tishan89]

Description: Single SP node with below as cluster config

cluster.config:
  enabled: false

will fail to start up with NPE.

Caused by: java.lang.NullPointerException
 at org.wso2.carbon.cluster.coordinator.rdbms.internal.RDBMSCoordinationServiceComponent.start(RDBMSCoordinationServiceComponent.java:59)
 ... 28 more

Ideally product should be able to start just with setting the configs to false.

Affected Product Version: 4.3.0

Steps to reproduce: Delete subsequent part of cluster.config and start the pack