Fix response_timeout

response_timeout is a method specific to a meterpreter session, not shell. So if the user is using a Msf::Sessions::CommandShell type payload, he will see a backtrace before interacting with the session.

This is kind of a serious bug. Please don't let it sit.

- [ ] Without the patch, this is how you can reproduce the problem:

```
./msfcli windows/smb/ms08_067_netapi rhost=[vuln host ip] payload=windows/shell_bind_tcp loglevel=3 E
```
- [ ] With the patch, you should be able to get a shell.
- [ ] Also test a meterpeter payload, and make sure that part is working properly still

Related to:
https://github.com/rapid7/metasploit-framework/pull/4442