Disable BLANK_PASSWORDS and USER_AS_PASS

They're as obnoxious as DB_ALL_* when enabled by default.

I do believe I have @jlee-r7's and @dmaloney-r7's support on this.

**Verification steps**

- [x] Use an ```AuthBrute``` module
- [x] Ensure that ```BLANK_PASSWORDS``` and ```USER_AS_PASS``` are ```false```
- [x] Run the module, preferably with a password that isn't the same as the username
- [x] See that the ```BLANK_PASSWORDS``` and ```USER_AS_PASS``` checks don't run

**Sample run**

```
msf > use auxiliary/scanner/ssh/ssh_login
msf auxiliary(ssh_login) > grep BLANK_PASSWORDS|USER_AS_PASS set
  BLANK_PASSWORDS       false
  USER_AS_PASS          false
msf auxiliary(ssh_login) > set RHOSTS 172.16.126.129
RHOSTS => 172.16.126.129
msf auxiliary(ssh_login) > set USERNAME msfadmin
USERNAME => msfadmin
msf auxiliary(ssh_login) > set PASSWORD trustno1
PASSWORD => trustno1
msf auxiliary(ssh_login) > run

[*] 172.16.126.129:22 SSH - Starting bruteforce
[*] 172.16.126.129:22 SSH - [1/1] - Trying: username: 'msfadmin' with password: 'trustno1'
[-] 172.16.126.129:22 SSH - [1/1] - Failed: 'msfadmin':'trustno1'
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
msf auxiliary(ssh_login) > unset PASSWORD 
Unsetting PASSWORD...
msf auxiliary(ssh_login) > set USER_AS_PASS true
USER_AS_PASS => true
msf auxiliary(ssh_login) > run

[*] 172.16.126.129:22 SSH - Starting bruteforce
[*] 172.16.126.129:22 SSH - [1/2] - Trying: username: 'msfadmin' with password: 'msfadmin'
[*] Command shell session 1 opened (172.16.126.1:46018 -> 172.16.126.129:22) at 2014-03-24 16:10:16 -0500
[+] 172.16.126.129:22 SSH - [1/2] - Success: 'msfadmin':'msfadmin' 'uid=1000(msfadmin) gid=1000(msfadmin) groups=4(adm),20(dialout),24(cdrom),25(floppy),29(audio),30(dip),44(video),46(plugdev),107(fuse),111(lpadmin),112(admin),119(sambashare),1000(msfadmin) Linux metasploitable 2.6.24-16-server #1 SMP Thu Apr 10 13:58:00 UTC 2008 i686 GNU/Linux '
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
msf auxiliary(ssh_login) > 
```