Add Wing FTP Server post-auth remote command execution module
Removed unused require and import. Handle the res.nil case in
execute_command() and authenticate().
Handle res.nil case in check(). Revert check for res.nil in
execute_command() because it was failing prior to the reverse_shell
connecting.
Fix failure messages for check().
Rename and apply rubocop style to wing_ftp_admin_exec
Land #3709, @nnam's wing ftp admin console cmd exec