Added new function to create a compose repo file

Requires the BASE_URL be passed in the command.

Example
```
$ BASE_URL=http://something.testurl.com fab -H satqe-collab.usersys.redhat.com -u root -p ***** generate_compose_repofile
$ cat compose.repo
[sat-upgrade]
name=sat-upgrade
baseurl=http://something.testurl.com
enabled=1
```
Adresses #72 
i was thinking about making it general, but don't know if this function would be useful outside of installing a compose.