Work around subprocess.run not having a capture_output param in old P…

…y3 versions. https://stackoverflow.com/questions/53209127/subprocess-unexpected-keyword-argument-capture-output

cattle/cattle_cli.py

@@ -114,7 +114,8 @@ def transfer(self, archive: str, executable: str, exec_dir: str):
         shutil.copy(executable, exec_dir)
 
     def exec_command(self, cmd: str):
-        proc = subprocess.run(cmd, capture_output=True, check=True, shell=True)
+        proc = subprocess.run(cmd, check=True, shell=True,
+                              stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         return proc.stdout.decode().strip()
 
 class HostRunner: