MINOR: Request log should be enabled by debug level

At some point, we lost the ability to output request
logging at debug level (which is a little less
verbose than at trace level).

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Jason Gustafson <jason@confluent.io>

Closes #3595 from ijuma/fix-debug-request-log

core/src/main/scala/kafka/network/RequestChannel.scala

@@ -198,7 +198,7 @@ object RequestChannel extends Logging {
         val apiThrottleTimeMs = nanosToMs(responseCompleteTimeNanos - apiRemoteCompleteTimeNanos)
         val responseQueueTimeMs = nanosToMs(responseDequeueTimeNanos - responseCompleteTimeNanos)
         val responseSendTimeMs = nanosToMs(endTimeNanos - responseDequeueTimeNanos)
-        requestLogger.trace("Completed request:%s from connection %s;totalTime:%f,requestQueueTime:%f,localTime:%f,remoteTime:%f,throttleTime:%f,responseQueueTime:%f,sendTime:%f,securityProtocol:%s,principal:%s,listener:%s"
+        requestLogger.debug("Completed request:%s from connection %s;totalTime:%f,requestQueueTime:%f,localTime:%f,remoteTime:%f,throttleTime:%f,responseQueueTime:%f,sendTime:%f,securityProtocol:%s,principal:%s,listener:%s"
           .format(requestDesc(detailsEnabled), connectionId, totalTimeMs, requestQueueTimeMs, apiLocalTimeMs, apiRemoteTimeMs, apiThrottleTimeMs, responseQueueTimeMs, responseSendTimeMs, securityProtocol, session.principal, listenerName.value))
       }
     }