Jenkins cli Ampersand Replacement Arbitrary File Read

This module utilizes the Jenkins cli protocol to run the `help` command.
The cli is accessible with read-only permissions by default, which are
all thats required.

Jenkins cli utilizes `args4j's` `parseArgument`, which calls `expandAtFiles` to
replace any `@` with the contents of a file. We are then able to retrieve
the error message to read up to the first two lines of a file.

Exploitation by hand can be done with the cli, see markdown documents for additional
instructions.

There are a few exploitation oddities:
1. The injection point for the `help` command requires 2 input arguments.
When the `expandAtFiles` is called, each line of the `FILE_PATH` becomes an input argument.
If a file only contains one line, it will throw an error: `ERROR: You must authenticate to access this Jenkins.`
However, we can pad out the content by supplying a first argument.
2. There is a strange timing requirement where the `download` (or first) request must get
to the server first, but the `upload` (or second) request must be very close behind it.
From testing against the docker image, it was found values between `.01` and `1.9` were
viable. Due to the round trip time of the first request and response happening before
request 2 would be received, it is necessary to use threading to ensure the requests
happen within rapid succession.

Files of value:
* /var/jenkins_home/secret.key
* /var/jenkins_home/secrets/master.key
* /var/jenkins_home/secrets/initialAdminPassword
* /etc/passwd
* /etc/shadow
* Project secrets and credentials
* Source code, build artifacts