Fix check command host selection behavior

[SeeRM #8768] Instead of using the saved value for host, the check command should use whatever the user specifies.

### Please verify the following ###

Scenario: The check command should use the RHOST option you specify instead of using whatever is in the config file.

- [x] Make sure you have a Win XP SP3 that's vulnerable to ms08_067_netapi for testing.
- [x] Run ```msfconsole```
- [x] Enter: ```use exploit/windows/smb/ms08_067_netapi```
- [x] Enter: ```set RHOST [IP 1]```
- [x] Enter: ```save```
- [x] Enter: ```set RHOST [IP 2]```
- [x] Enter: ```check```
- [x] Confirm that the check command runs against IP 2, and not IP 1.

Scenario: The check command should still use the saved option if it isn't specified by the user.

- [x] Make sure you still have the saved RHOST option (IP 1) from the previous test.
- [x] Make sure you're in ```msfconsole```
- [x] Make sure you're in ```exploit/windows/smb/ms08_067_netapi```
- [x] Enter: ```check```
- [x] Confirm that the check command runs against IP 1.