Checks that if there are external instances, the master is
one of them

@param {String} masterId  - Instance ID of master
@param {Object} instances - Instances map

@returns {Boolean} True if there are no external instances or
if there are external instances and the master is
one of them
function isMasterExternalValueOk(masterId, instances) {
        const instanceIds = Object.keys(instances);
        let instance;
        let hasExternal;

        for (let i = 0; i < instanceIds.length; i++) {
            instance = instances[instanceIds[i]];
            if (instance.external) {
                hasExternal = true;
                break;
            }
        }

        if (hasExternal) {
            return !!instances[masterId].external;
        }

        return true;
    }