nixos-rebuild: fix --use-remote-sudo

Currently fails with:

  $ nixos-rebuild test --target-host myhost --use-remote-sudo
  building Nix...
  sudo: /run/current-system/sw/bin/sudo must be owned by uid 0 and have the setuid bit set

It seems setting an explicit PATH in the ssh command overrides the
remote setuid wrappers.

(cherry picked from commit 35a8d78e44d566d6d2ddba42ae5137f7a511a090)

pkgs/os-specific/linux/nixos-rebuild/nixos-rebuild.sh

@@ -145,7 +145,7 @@ buildHostCmd() {
     if [ -z "$buildHost" ]; then
         "$@"
     elif [ -n "$remoteNix" ]; then
-        ssh $SSHOPTS "$buildHost" env PATH="$remoteNix":'$PATH' "${maybeSudo[@]}" "$@"
+        ssh $SSHOPTS "$buildHost" "${maybeSudo[@]}" env PATH="$remoteNix":'$PATH' "$@"
     else
         ssh $SSHOPTS "$buildHost" "${maybeSudo[@]}" "$@"
     fi