Support RHOSTS for msfcli (C)heck mode

One of my favorite users, @sho-luv, noticed that RHOSTS doesn't work when you want to run a (C)heck from msfcli.

I've addressed this by simply stomping on the RHOST field and iterating over the given RHOSTS option. Since msfcli is a oneshot, we don't need to worry about preserving RHOST after the run on the module.

## Verification

Run the following commands, using your own preferred IP addresses.

- [ ] Demonstrate concatination of RHOST and RHOSTS, and the nmap-style comma-seperated last octets.: `./msfcli exploit/windows/smb/ms08_067_netapi RHOST=10.1.1.1 RHOSTS=192.168.145.60,191,137 C` 
- [ ]  Demo CIDR notation: `./msfcli exploit/windows/smb/ms08_067_netapi RHOST=10.1.1.1 RHOSTS=192.168.145.60/30 C`
- [ ]  Demo that RHOST is not necessary to set (since we're doing it internally): `./msfcli exploit/windows/smb/ms08_067_netapi RHOSTS=192.168.145.60,137 C`
- [ ] Demos hyphen ranges: `./msfcli exploit/windows/smb/ms08_067_netapi RHOSTS=192.168.145.59-61 C`

## Expected Results:

````
[ruby-1.9.3-p484@metasploit-framework] (multicheck-msfcli-compat) 
todb@mazikeen:~/git/rapid7/metasploit-framework
$ ./msfcli exploit/windows/smb/ms08_067_netapi RHOST=10.1.1.1 RHOSTS=192.168.145.60,191,137 C
[*] Initializing modules...
[*] Checking 10.1.1.1, 192.168.145.60,191,137
[*] 10.1.1.1:445 - Cannot reliably check exploitability.
[+] 192.168.145.60:445 - The target is vulnerable.
[*] 192.168.145.137:445 - The target is not exploitable.
[*] 192.168.145.191:445 - The target is not exploitable.

[ruby-1.9.3-p484@metasploit-framework] (multicheck-msfcli-compat) 
todb@mazikeen:~/git/rapid7/metasploit-framework
$ ./msfcli exploit/windows/smb/ms08_067_netapi RHOST=10.1.1.1 RHOSTS=192.168.145.60/30 C
[*] Initializing modules...
[*] Checking 10.1.1.1, 192.168.145.60/30
[*] 10.1.1.1:445 - Cannot reliably check exploitability.
[+] 192.168.145.60:445 - The target is vulnerable.
[*] 192.168.145.61:445 - Cannot reliably check exploitability.
[*] 192.168.145.62:445 - Cannot reliably check exploitability.
[*] 192.168.145.63:445 - Cannot reliably check exploitability.

[ruby-1.9.3-p484@metasploit-framework] (multicheck-msfcli-compat) 
todb@mazikeen:~/git/rapid7/metasploit-framework
$ ./msfcli exploit/windows/smb/ms08_067_netapi RHOSTS=192.168.145.60,137 C
[*] Initializing modules...
[*] Checking 192.168.145.60,137
[+] 192.168.145.60:445 - The target is vulnerable.
[*] 192.168.145.137:445 - The target is not exploitable.

[ruby-1.9.3-p484@metasploit-framework] (multicheck-msfcli-compat) 
todb@mazikeen:~/git/rapid7/metasploit-framework
$ ./msfcli exploit/windows/smb/ms08_067_netapi RHOSTS=192.168.145.59-61 C
[*] Initializing modules...
[*] Checking 192.168.145.59-61
[*] 192.168.145.59:445 - Cannot reliably check exploitability.
[+] 192.168.145.60:445 - The target is vulnerable.
[*] 192.168.145.61:445 - Cannot reliably check exploitability.

[ruby-1.9.3-p484@metasploit-framework] (multicheck-msfcli-compat) 
todb@mazikeen:~/git/rapid7/metasploit-framework
$ 
````

## Caveats

the `file:/path/to/file` format is not supported in this mode -- but it's not supported in the usual `msfconsole` implementation either. So... not a new bug, no missing functionality.