unified travis script to handle different branches

Factor it out?
```bash
REPO="YaST:SLE-12:GA"
REPO_URL="http://download.opensuse.org/repositories/${REPO//:/:/}:/Travis/xUbuntu_12.04/"
```

(obscure shell substitution could be made simpler by using `REPO_PART="YaST:/SLE-12:/GA"`