Feature/msp 10992/scanner dry

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