Use text=true in subprocess

ext_scripts/ext_rbd.py

@@ -66,7 +66,7 @@ PREFIX_USP = 'usp_'
 def cmd_open(cmd, bufsize=-1, env=None):
     inst = subprocess.Popen(cmd, shell=False, bufsize=bufsize,
                             stdin=subprocess.PIPE, stdout=subprocess.PIPE,
-                            stderr=subprocess.PIPE, close_fds=True)
+                            stderr=subprocess.PIPE, close_fds=True, text=True)
     return inst