Add `log-level` mount option support for glusterfs plugin

The glusterfs plugin/driver set log-level to ERROR by default while
mounting glusterfs shares. However at times, its required to supply other
log-level options like INFO, TRACE..etc. This patch enables the support
to provide other log-level values from storageclass.

Additional Ref#
    https://docs.gluster.org/en/v3/Administrator%20Guide/Setting%20Up%20Clients/

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>

pkg/volume/glusterfs/glusterfs.go

@@ -290,6 +290,7 @@ func (b *glusterfsMounter) setUpAtInternal(dir string) error {
 	var errs error
 	options := []string{}
 	hasLogFile := false
+	hasLogLevel := false
 	log := ""
 
 	if b.readOnly {
@@ -297,13 +298,19 @@ func (b *glusterfsMounter) setUpAtInternal(dir string) error {
 
 	}
 
-	// Check logfile has been provided by user, if provided, use that as the log file.
+	// Check for log-file,log-level options existence in user supplied mount options, if provided, use those.
 	for _, userOpt := range b.mountOptions {
-		if dstrings.HasPrefix(userOpt, "log-file") {
+
+		switch {
+		case dstrings.HasPrefix(userOpt, "log-file"):
 			glog.V(4).Infof("log-file mount option has provided")
 			hasLogFile = true
-			break
+
+		case dstrings.HasPrefix(userOpt, "log-level"):
+			glog.V(4).Infof("log-level mount option has provided")
+			hasLogLevel = true
 		}
+
 	}
 
 	// If logfile has not been provided, create driver specific log file.
@@ -324,7 +331,9 @@ func (b *glusterfsMounter) setUpAtInternal(dir string) error {
 
 	}
 
+	if !hasLogLevel {
 		options = append(options, "log-level=ERROR")
+	}
 
 	var addrlist []string
 	if b.hosts == nil {