MINOR: Change log level for group member failure from debug to info

Author: Guozhang Wang <wangguoz@gmail.com>

Reviewers: Jason Gustafson <jason@confluent.io>

Closes #3523 from guozhangwang/KMinor-group-coordinator-member-failure-info-log4j

core/src/main/scala/kafka/coordinator/group/GroupCoordinator.scala

@@ -320,7 +320,8 @@ class GroupCoordinator(val brokerId: Int,
             } else {
               val member = group.get(memberId)
               removeHeartbeatForLeavingMember(group, member)
-              onMemberFailure(group, member)
+              debug(s"Member ${member.memberId} in group ${group.groupId} has left, removing it from the group")
+              removeMemberAndUpdateGroup(group, member)
               responseCallback(Errors.NONE)
             }
           }
@@ -692,8 +693,7 @@ class GroupCoordinator(val brokerId: Int,
     joinPurgatory.tryCompleteElseWatch(delayedRebalance, Seq(groupKey))
   }
 
-  private def onMemberFailure(group: GroupMetadata, member: MemberMetadata) {
-    debug(s"Member ${member.memberId} in group ${group.groupId} has failed")
+  private def removeMemberAndUpdateGroup(group: GroupMetadata, member: MemberMetadata) {
     group.remove(member.memberId)
     group.currentState match {
       case Dead | Empty =>
@@ -774,8 +774,10 @@ class GroupCoordinator(val brokerId: Int,
 
   def onExpireHeartbeat(group: GroupMetadata, member: MemberMetadata, heartbeatDeadline: Long) {
     group synchronized {
-      if (!shouldKeepMemberAlive(member, heartbeatDeadline))
-        onMemberFailure(group, member)
+      if (!shouldKeepMemberAlive(member, heartbeatDeadline)) {
+        info(s"Member ${member.memberId} in group ${group.groupId} has failed, removing it from the group")
+        removeMemberAndUpdateGroup(group, member)
+      }
     }
   }