chapi: busy or already mounted nfs mounts should be successfull (#153)

Problem:
- just like regular pvc mounts, if the mounts for the volume already exist(
the previous commands times out) we treat the subsequent mount as success if the same
source and target are present. The same logic was missing for nfs mounts.

Signed-off-by: Raunak <[email protected]>

Author: raunakkumar

linux/mount.go

@@ -589,6 +589,17 @@ func MountNFSShare(source string, targetPath string, options []string, nfsType s
 		nfsType = defaultNFSType
 	}
 
+	mountedSource := GetDeviceFromMountPoint(targetPath)
+	if mountedSource != "" {
+		// the source exists for the target path but differs from the expected mount, return error
+		if mountedSource != source {
+			err := fmt.Errorf("%s is already mounted at %s. Skipping mount for %s", mountedSource, source, targetPath)
+			return err
+		}
+		// if mount point present with expected targetPath, return successful
+		return nil
+	}
+
 	args := []string{fmt.Sprintf("-t%s", nfsType), source, targetPath}
 	optionArgs := []string{}
 	if len(options) != 0 {