Added ssh, core user and /etc/environment

Fleet is only usable with ssh. So it is enabled by default and the
container can be accessed via core:coreos. Since conair configures
container networking via dhcp the ip is now available through
/etc/environment.
Merge branch 'master' of github.com:teemow/conair-coreos

* 'master' of github.com:teemow/conair-coreos:
  README: add chmod +x to the script