Added new function to create/add to a custom automation-tools repo file
Required the repo_url be passed in the command.
Example
-------
```
$ fab -H satqe-collab.usersys.redhat.com -u root -p '******' add_repo:'http://porkchop.devel.redhat.com/released/RHEL-7/7.0/Server/x86_64/os/'
$ cat automation-tools.repo
[porkchop.devel.redhat.com]
name=porkchop.devel.redhat.com
baseurl=http://porkchop.devel.redhat.com/released/RHEL-7/7.0/Server/x86_64/os/
enabled=1
```