Minimize rebuilds in makefile
Minimize rebuilds in makefile

Take advantage of make dependency tracking and that `--link` doesn't require
the link be *valid* in order to reduce rebuilds of prereq targets.

- `build` is a target with only dependencies; build/containerbuddy always ends
  up being newer than the build/ dir otherwise and we always rebuild.
- `integration` only requires the finished Containerbuddy binary, not etc or
  consul; the integration tests stand up discovery as-needed
- `lint` only requires the builder, not etcd/consul

flyinprogrammer/containerpilot,joyent/containerbuddy,flyinprogrammer/containerpilot,benoittoulme/containerpilot,tgross/containerbuddy,justenwalker/containerbuddy,joyent/containerpilot,benoittoulme/containerpilot,justenwalker/containerbuddy,joyent/containerpilot,joyent/containerbuddy,joyent/containerpilot,justenwalker/containerpilot,benoittoulme/containerpilot,justenwalker/containerpilot,tgross/containerbuddy