Fix Salt decode error (#636)

* Fix #398 `salt` backend returning non-encoded strings

`salt` backend failed because local satl client returns
`stdout` and `stderr` as `str` objects not encoded `bytes`.

Taking a lead from the `ansible` implementation the `stdout` and
`stderr` results are both encoded and returned as `kwargs` through
`base.result` method.


Co-authored-by: Mark Bools <[email protected]>

Author: Sander Cornelissen

testinfra/backend/salt.py

@@ -36,7 +36,14 @@ def client(self):
     def run(self, command, *args, **kwargs):
         command = self.get_command(command, *args)
         out = self.run_salt("cmd.run_all", [command])
-        return self.result(out["retcode"], command, out["stdout"], out["stderr"])
+        return self.result(
+            out["retcode"],
+            command,
+            out["stdout"].encode("utf8"),
+            out["stderr"].encode("utf8"),
+            stdout=out["stdout"],
+            stderr=out["stderr"],
+        )
 
     def run_salt(self, func, args=None):
         out = self.client.cmd(self.host, func, args or [])