chore(*): update CoreOS to 440.0.0

https://coreos.com/releases/#440.0.0
chore(*/systemd): remove deprecated X-Condition in fleet units
Merge pull request #1845 from carmstrong/remove_deprecated_condition

chore(*/systemd): remove deprecated X-Condition in fleet units
Merge pull request #1844 from carmstrong/coreos-440.0.0

chore(*): update CoreOS to 440.0.0
refactor(makefile): remove fleet, switch to deisctl and custom images
fix(user-data): restore default discovery url
docs(readme): update root readme with new deisctl instructions
docs(hacking): new docs for hacking on deis
fix(readme): address feedback, fix typos
fix(makefile): default to 3 nodes, test for docker binary
docs(readme): add hack instructions to readme, remove newline
ref(Makefiles): use $BUILD_TAG, which defaults to "git rev-parse"
ref(tests): use images from "make build" in component tests
fix(user-data): add fixed version of sed command to "make discovery-url"