actions: fix fstab generated in case of FAT{12|16|32}.

Recent changes introduced a tuned formatting of the partitions created
with FAT{12|16|32}. The issue is that fstab is generated using the fs
property which won't match the system expectations.

If the fs property is "fat", "fat12", "fat16", "fat32" or "msdos", then
fstab must use "vfat".

Signed-off-by: Aymen Zayet <aymen.zayet@flex.ai>

actions/image_partition_action.go

@@ -270,8 +270,17 @@ func (i *ImagePartitionAction) generateFSTab(context *debos.DebosContext) error
 				fs_passno = 2
 			}
 		}
+
+		fsType := m.part.FS
+		switch m.part.FS {
+			case "fat", "fat12", "fat16", "fat32", "msdos":
+				fsType = "vfat"
+			default:
+				break
+		}
+
 		context.ImageFSTab.WriteString(fmt.Sprintf("UUID=%s\t%s\t%s\t%s\t0\t%d\n",
-			m.part.FSUUID, m.Mountpoint, m.part.FS,
+			m.part.FSUUID, m.Mountpoint, fsType,
 			strings.Join(options, ","), fs_passno))
 	}