Feature/msp 10992/scanner dry

VERIFICATION STEPS
- [x] check out the metasploit-credential branch at https://github.com/rapid7/metasploit-credential/pull/68
- [x] point your gemfile for credential to your local path
- [x] `msfconsole`
- [x] `use auxiliary/scanner/ssh/ssh_login`
- [x] `set RHOSTS 10.20.37.50`
- [x] `set username msfadmin`
- [x] `set password msfadmin`
- [x] `run`
- [x] VERIFY the module doesn't blow up (except maybe for that private already taken bug)
- [x] VERIFY successful creds were added
- [x] check any other login module you might want