rbd: rbd-nbd logging the ceph-CSI way

- One logfile per device/volume
- Add ability to customize the logdir, default: /var/log/ceph

Note: if user customizes the hostpath to something else other than default
/var/log/ceph, then it is his responsibility to update the `cephLogDir`
in storageclass to reflect the same with daemon:

```
cephLogDir: "/var/log/mynewpath"
```

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>

internal/rbd/rbd_util.go

@@ -50,6 +50,7 @@ const (
 	rbdImageWatcherSteps     = 10
 	rbdDefaultMounter        = "rbd"
 	rbdNbdMounter            = "rbd-nbd"
+	defaultLogDir            = "/var/log/ceph"
 
 	// Output strings returned during invocation of "ceph rbd task add remove <imagespec>" when
 	// command is not supported by ceph manager. Used to check errors and recover when the command
@@ -136,6 +137,7 @@ type rbdVolume struct {
 	ReservedID         string
 	MapOptions         string
 	UnmapOptions       string
+	LogDir             string
 	VolName            string `json:"volName"`
 	MonValueFromSecret string `json:"monValueFromSecret"`
 	VolSize            int64  `json:"volSize"`
@@ -2002,3 +2004,16 @@ func (ri *rbdImage) addSnapshotScheduling(
 
 	return nil
 }
+
+// getCephClientLogFileName compiles the complete log file path based on inputs.
+func getCephClientLogFileName(id, logDir, prefix string) string {
+	if prefix == "" {
+		prefix = "ceph"
+	}
+
+	if logDir == "" {
+		logDir = defaultLogDir
+	}
+
+	return fmt.Sprintf("%s/%s-%s.log", logDir, prefix, id)
+}