Adds osx vmware/bash priv escalation.

Adds a module for getting root on osx+vmware, by abusing the bash bug. Thanks to juken for reporting this in freenode#metasploit!

##### Verification
- [ ] get a user shell session on osx with VMWare Fusion installed
- [ ] run the local exploit module:

        msf> use exploit/osx/local/vmware_bash_function_root
        msf> set SESSION 1
        msf> run

- [ ] You should get a root shell.
Won't File.join behave differently on Windows? Or do we override it somehow