fixed crash on failed command execution

sau/helpers.py

@@ -12,6 +12,9 @@ def exec_cmd(cmd, timeout=900, env = None):
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             env = env)
+    out = b""
+    err = b""
+
     try:
         out, err = proc.communicate(timeout=timeout)
     except subprocess.TimeoutExpired as err:
@@ -22,7 +25,6 @@ def exec_cmd(cmd, timeout=900, env = None):
             log.error('Command "{}" would not be killed, forcing a termination'.format(' '.join(cmd)))
             proc.terminate()
             time.sleep(5)
-
     return (proc.returncode, out.decode('utf-8'), err.decode('utf-8'))