add better error message

zfs_backup.py

@@ -605,8 +605,7 @@ class Cryptsetup(CommandInterface):
                 device = Path(line.split(":")[-1].strip())
                 break
         else:
-            # TODO better error message
-            print("panic")
+            print(Messages.CANNOT_FIND_DEVICE_PATH)
             exit(EXIT_ERROR)
         # noinspection PyUnboundLocalVariable
         return device
@@ -830,6 +829,7 @@ class CommandRunner:
 class Messages:
     ALREADY_DECRYPTED = "Cannot decrypt, already decrypted"
     ALREADY_IMPORTED = "Cannot import, already imported"
+    CANNOT_FIND_DEVICE_PATH = "Cannot find device path from output of `cryptsetup status`"
     CANNOT_FIND_BACKUP_DRIVE = "Could not find a backup drive"
     DELETE_IN_LOCAL_POOL = "ALERT! Tried to delete in local pool!"
     MAPPER_ENTRY_ALREADY_EXISTS = "mapper entry already exists"