feat(coreos-base/coreos): Add btrfs-progs
feat(coreos-base/coreos): Add brctl

It would be nice if it was possible to look at the state of the docker0
bridge, so here is the proper tool to do that.
Merge pull request #397 from marineam/btrfs

feat(coreos-base/coreos): Add btrfs-progs and brctl