Credential Gem: LoginScanner - vmauthd_login ( Rebase of PR 3608)

This PR is a rebase of PR #3608 that was required after the Metasploit Electro branch was merged into Master.

It is a refactor of vmauthd_login.rb to support the Metasploit Credential gem

**Verification**

- [ ] ````msfconsole````
- [ ] ````use auxiliary/scanner/vmware/vmauthd_login````
- [ ] ````set RHOSTS ,<vmware_host>````
- [ ] ````set USERNAME root````
- [ ] ````set PASSWORD <valid_password>````
- [ ] ````run````
     - [ ]  Scan results should be printed
- [ ]  ````creds````
- [ ]  __VERIFY__ that credentials identified in the scan output are found in the results from creds

Repeat the process using USER_FILE, PASS_FILE, etc.