make call() python 3.6 compatible

zfs-snapshot-backup.py

@@ -13,9 +13,9 @@ ZFS_ELAB_PREFIX = "elabfs-"
 TMP_BACKUP_FOLDER = "/mnt/Datenspeicher/snap-backup-dataset/temporary-backups"
 
 
-def call(arguments):
+def call(arguments, as_text=False):
     result = subprocess.run(
-        arguments, check=True, capture_output=True, text=True
+        arguments, check=True, stdout=subprocess.PIPE, universal_newlines=as_text
     )
     return result.stdout
 
@@ -23,7 +23,7 @@ def call(arguments):
 def remote_call(arguments):
     cmd = ["ssh", "-i", SSH_KEY_FILE, SSH_REMOTE]
     cmd.extend(arguments)
-    return call(cmd)
+    return call(cmd, as_text=True)
 
 
 def clean_split(text):