Fix #4695, allow ms09_067_excel_featheader to save file

[jvazquez-r7]

According to my analysis ms09_067_excel_featheader is not missing nothing, on my system, just trying to write to a nonexistent directory. I've fixed the default value for OUTPUTPATH to use Msf::Config.local_directory as FILEFORMAT mixin does.

Verification

• Init the console
• use exploit/windows/fileformat/ms09_067_excel_featheader
• set TARGET 4
• exploit verify which it doesn't raise errors:

msf exploit(ms09_067_excel_featheader) > rexploit
[*] Reloading module...

[*] Creating Excel spreadsheet ...
[*] Generated output file /Users/jvazquez/.msf4/local/msf.xls

• exit the console and verify which the file exists:

msf exploit(ms09_067_excel_featheader) > exit -y
AUS-MAC-0916:metasploit-framework jvazquez$ file /Users/jvazquez/.msf4/local/msf.xls
/Users/jvazquez/.msf4/local/msf.xls: CDF V2 Document, No summary info

[jvazquez-r7]

Fixes #4695