Revert "loader/lua: Remove workaround for command_error"

This reverts commit 552f3072af54820cf1805f712e2567bc1b7f046d.

loader.command_error was added just after 11.2, but appears to not have
been back ported to 11.x. 11.0 was the first lua loader release, so keep
this compat shim until we sort out what to do.

MFC After: 3 days
Sponsored by: Netflix
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D45883