Add WIP documentation for auxiliary/scanner/mqtt/connect

documentation/modules/auxiliary/scanner/mqtt/connect.md

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+## Vulnerable Application
+
+Most any MQTT instance will work.  Instructions for testing against a Dockerized endpoint are provided below.
+
+### Docker Install
+
+A dockerized version of [mosquitto](https://mosquitto.org/) is available
+[here](https://github.com/toke/docker-mosquitto).  There are two basic
+scenarios worth discussing -- mosquitto with anonymous authentication allowed
+and disallowed.  The method for running both is similar.
+
+#### Docker MQTT Server With Anonymous Authentication
+
+By default, mosquitto does not require credentials and allows anonymous authentication.  To run in this way:
+
+```
+$  docker run -i -p 1883:1883  toke/mosquitto
+1513822879: mosquitto version 1.4.14 (build date Mon, 10 Jul 2017 23:48:43 +0100) starting
+1513822879: Config loaded from /mqtt/config/mosquitto.conf.
+1513822879: Opening websockets listen socket on port 9001.
+1513822879: Opening ipv4 listen socket on port 1883.
+1513822879: Opening ipv6 listen socket on port 1883.
+```
+
+#### Docker MQTT Server Without Anonymous Authenticaiton
+
+Msquitto can be configured to require credentials.  To run in this way:
+
+  1. Create a simple configuration file:
+  ````
+  $  mkdir -p config && cat > config/mosquitto.conf
+  password_file /mqtt/config/passwd
+  allow_anonymous false
+  ```
+  2. Create a password file for mosquitto (this example creates a user test_user with password test_pass)
+  ```
+  $  touch config/passwd && mosquitto_passwd -b config/passwd test_user test_pass
+  ```
+  1. Now run the dockerized mosquitto instance, mounting the configuration files from above for use at runtime:
+  ```
+  $  docker run -ti -p 1883:1883 -v `pwd`/config/:/mqtt/config:ro  toke/mosquitto
+  1513823564: mosquitto version 1.4.14 (build date Mon, 10 Jul 2017 23:48:43 +0100) starting
+  1513823564: Config loaded from /mqtt/config/mosquitto.conf.
+  1513823564: Opening ipv4 listen socket on port 1883.
+  1513823564: Opening ipv6 listen socket on port 1883.
+  ```
+
+## Verification Steps
+
+
+  1. Install the application without credentials
+  2. Start msfconsole
+  3. Do: ```use auxiliary/scanner/mqtt/connect```
+  4. Do: ```set rhosts [IPs]```
+  5. Do: ```run```
+  6. Confirm that the default or non-default credentials are discovered as configured
+
+## Options
+
+  **CLIENT_ID**
+
+  When specified, this will set the ID of the client when connecting to the MQTT endpoint.  While
+  not all MQTT implementation support this, some, like mosquitto, support filtering by client ID and
+  this option can be used in those scenarios.  By default, a random ID is selected.
+
+## Scenarios
+
+### Docker MQTT Server Without Credentials
+```
+```
+
+### Docker MQTT Server With Credentials
+```
+```