Attack plugins: Add support for duplicated command output in response body

[andresriancho]

Introduction

Attack plugins should support the case when the application returns the expected command output more than once. The problem looks like this:

Works

http://localhost/foo?cmd=whoami
...
root

Doesn't work

http://localhost/foo?cmd=whoami
...
root
...
root
...
root

Conditions of satisfaction

• Write a django-moth test with os_commanding
• Write a unittest showing that it doesn't work
• Fix it to work with 1-N copies of the command output in the HTTP response body