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 
What about other environ variable name? If this will be used when installing a compose build then `BASE_URL` will be the URL for the installation and not for the upgrade.