Added new function to create a compose repo file

Requires the repo_url be passed in the command.
Example
-------
```
fab -H ibm-x3550m3-12.lab.eng.brq.redhat.com -u root -p '******' add_repo:'test','http://porkchop.devel.redhat.com/released/RHEL-7/7.0/Server/x86_64/os/';
[ibm-x3550m3-12.lab.eng.brq.redhat.com] Executing task 'add_repo'
[ibm-x3550m3-12.lab.eng.brq.redhat.com] run: echo "[test]
name=test
baseurl=http://porkchop.devel.redhat.com/released/RHEL-7/7.0/Server/x86_64/os/
enabled=1
" >> automation-tools.repo
```
Adresses #72 
What about failing the task or maybe printing a warning if repo_url is None? I think that adding a repo is a required step and would be better to fail if no repo_url are not provided.