Restore 'Proxies' option for LoginScanners

Fixes #3963 and #3959.

#### Verification
 - [ ] `ssh localhost -D 1080 -nNTvv`
 - [ ] in another terminal, open msfconsole
 - [ ] `use auxiliary/scanner/ssh/ssh_login`
 - [ ] `set Proxies socks4:localhost:1080-socks5:localhost:1080`
 - [ ] set other options as appropriate
 - [ ] `run`
 - [ ] **Verify** ssh shows a connection to localhost (for the second proxy line) and then to RHOSTS
 - [ ] `use auxiliary/scanner/ssh/http_login`
 - [ ] `set Proxies socks4:localhost:1080-socks5:localhost:1080`
 - [ ] set other options as appropriate
 - [ ] `run`
 - [ ] **Verify** ssh shows a connection to localhost (for the second proxy line) and then to RHOSTS


Where does "proxies" come from?? I am getting a NameError undefined local variable or method for this.