Small improvements

Small improvements:
1. Adding a gitignore that hides galaxy install info. usefull if one installs the role via galaxy first and then starts to check it out in place to hack on it.
2. Soften the access permissions for the automatic upgrades script slightly. Now users of the adm group can use apt-cache again
3. apt-get update with caching. There are often many roles that want to update the cache, this can be a pita. the cache rule takes care that if another role already ran an update, this won't update too. (7200 seconds, iow 2 hours cache)