pid is not extracted correctly in "attack_broker.py" file

In the file "attack_broker.py" the following two lines(line 102-103) attempt to execute a subprocess and extracts its pid.

```
    child = subprocess.Popen('pgrep xterm', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, executable='/bin/bash')
    pid = int(child.communicate()[0].split('\n')[0])
``` 

However, this doesn't give the correct pid.

