MDC logging does not work with camel.routeId when using exchange.addOnCompletion(...).

Issue

• User migrated from camel 2.12 to 2.15 (Fuse 6.1 to Fuse 6.2) and noticed that his MDC logging didn't work anymore.
• When user removed {camel.routeId} from the logging definition, all worked again.
• Following are the logger configurations

log4j.appender.audit=org.apache.log4j.sift.MDCSiftingAppender
log4j.appender.audit.key=camel.contextId
log4j.appender.audit.default=unknown
log4j.appender.audit.appender=org.apache.log4j.RollingFileAppender
log4j.appender.audit.appender.layout=org.apache.log4j.PatternLayout
log4j.appender.audit.appender.layout.ConversionPattern=%d{yyyy-MM-dd'T'HH:mm:ss,SSSXXX} | %-5.5p | %X{camel.routeId} %X{bundle.version} | %X{camel.breadcrumbId} | %X{messageType} | %m%n
log4j.appender.audit.appender.file=${karaf.data}/log/audit-$\\{camel.contextId\\}.log
log4j.appender.audit.appender.append=true
log4j.appender.audit.appender.maxFileSize=10MB
log4j.appender.audit.appender.maxBackupIndex=50

• Following is the route

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0"
    xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

        <bean id="myLogger" class="org.slf4j.LoggerFactory" factory-method="getLogger" >
                <argument value="auditLogger" />
        </bean>

        <bean id="onCompletionLogger" class="example.SimpleOnCompletionLogger">
                <argument ref="myLogger" />
        </bean>

    <camelContext id="myContextId" xmlns="http://camel.apache.org/schema/blueprint" useMDCLogging="true">
        <route id="myRouteId">
                <from uri="timer://foo?period=5s"/>
                <onCompletion>
                        <process ref="onCompletionLogger"/>
                </onCompletion>
                <log message="Logging test ${body}" loggerRef="myLogger"/>
        </route>
    </camelContext>
</blueprint>

• Following way the processor is implemented

public class SimpleOnCompletionLogger implements Processor {
    private Logger logger;

    public SimpleOnCompletionLogger(Logger logger) {
        this.logger = logger;
    }

    @Override
    public void process(Exchange exchange) throws Exception {
        exchange.addOnCompletion(new Synchronization() {

            @Override
            public void onComplete(Exchange exchange) {
                // LoggerFactory.getLogger("auditLogger").info("onComplete");
                logger.info("onComplete");
            }

            @Override
            public void onFailure(Exchange exchange) {
                logger.info("onFailure");
            }
        });
    }
}

• Logs are printed in following manner, here it can be seen that for one case routeId is not printed.

11:20:06,337 | INFO  | 72 - timer://foo | ROUTE_ID:myRouteId | auditLogger                      | Logging test
11:20:06,337 | INFO  | 72 - timer://foo | ROUTE_ID: | auditLogger                      | onComplete>