pass --log-json to remote

Obviously this means that --log-json with remote repos requires 1.1
on the remote end, but if you don't have that, then random "Remote:"
lines would break stderr anyway.

src/borg/logger.py

@@ -92,7 +92,7 @@ def setup_logging(stream=None, conf_fname=None, env_var='BORG_LOGGING_CONF', lev
         fmt = '$LOG %(levelname)s %(name)s Remote: %(message)s'
     else:
         fmt = '%(message)s'
-    formatter = JsonFormatter(fmt) if json else logging.Formatter(fmt)
+    formatter = JsonFormatter(fmt) if json and not is_serve else logging.Formatter(fmt)
     handler.setFormatter(formatter)
     borg_logger = logging.getLogger('borg')
     borg_logger.formatter = formatter

src/borg/remote.py

@@ -636,6 +636,12 @@ This problem will go away as soon as the server has been upgraded to 1.0.7+.
                 opts.append('--critical')
             else:
                 raise ValueError('log level missing, fix this code')
+            try:
+                borg_logger = logging.getLogger('borg')
+                if borg_logger.json:
+                    opts.append('--log-json')
+            except AttributeError:
+                pass
         env_vars = []
         if yes(env_var_override='BORG_HOSTNAME_IS_UNIQUE', env_msg=None, prompt=False):
             env_vars.append('BORG_HOSTNAME_IS_UNIQUE=yes')