logging: Log only for unhandled errors, remove all the debug logging. (#1652)

This patch brings in the removal of debug logging altogether, instead
we bring in the functionality of being able to trace the errors properly
pointing back to the origination of the problem.

To enable tracing you need to enable "MINIO_TRACE" set to "1" or "true"
environment variable which would print back traces whenever there is an
error which is unhandled or at the handler layer.

By default this tracing is turned off and only user level logging is
provided.

object-common-multipart.go

@@ -27,7 +27,6 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/skyrings/skyring-common/tools/uuid"
 )
 
@@ -306,12 +305,6 @@ func listMetaBucketMultipartFiles(layer ObjectLayer, prefixPath string, markerPa
 		}
 		// For any walk error return right away.
 		if walkResult.err != nil {
-			log.WithFields(logrus.Fields{
-				"bucket":    minioMetaBucket,
-				"prefix":    prefixPath,
-				"marker":    markerPath,
-				"recursive": recursive,
-			}).Debugf("Walk resulted in an error %s", walkResult.err)
 			// File not found or Disk not found is a valid case.
 			if walkResult.err == errFileNotFound || walkResult.err == errDiskNotFound {
 				return nil, true, nil
@@ -326,9 +319,6 @@ func listMetaBucketMultipartFiles(layer ObjectLayer, prefixPath string, markerPa
 			// entries are empty.
 			entries, err = listLeafEntries(storage, fi.Name)
 			if err != nil {
-				log.WithFields(logrus.Fields{
-					"prefixPath": fi.Name,
-				}).Errorf("%s", err)
 				return nil, false, err
 			}
 		}
@@ -442,12 +432,6 @@ func listMultipartUploadsCommon(layer ObjectLayer, bucket, prefix, keyMarker, up
 	// List all the multipart files at prefixPath, starting with marker keyMarkerPath.
 	fileInfos, eof, err := listMetaBucketMultipartFiles(layer, multipartPrefixPath, multipartMarkerPath, recursive, maxUploads)
 	if err != nil {
-		log.WithFields(logrus.Fields{
-			"prefixPath": multipartPrefixPath,
-			"markerPath": multipartMarkerPath,
-			"recursive":  recursive,
-			"maxUploads": maxUploads,
-		}).Errorf("listMetaBucketMultipartFiles failed with %s", err)
 		return ListMultipartsInfo{}, err
 	}
 
@@ -552,9 +536,8 @@ func isUploadIDExists(storage StorageAPI, bucket, object, uploadID string) bool
 		if err == errFileNotFound {
 			return false
 		}
-		log.Errorf("StatFile failed wtih %s", err)
+		errorIf(err, "Stat failed on "+minioMetaBucket+"/"+uploadIDPath+".")
 		return false
 	}
-	log.Debugf("FileInfo: %v", st)
 	return st.Mode.IsRegular()
 }