scripts: build ACI image using acbuild
scripts: build ACI image using acbuild

Various changes on build-aci.

* Use acbuild command for building the ACI image.
* Remove unnecessary docker command. Actually we could build ACI
  image without relying on docker, just like etcd does.
* Remove unnecessary manifest definition, as it's automatically
  generated by acbuild.
* Improve the cleanup path using acbuildEnd().
* Allow TCP ports 2379,4001 for etcd

How to test, for example:

$ ./scripts/build-aci v0.12.0-amd64
$ sudo rkt run --insecure-options=image \
  --stage1-name=coreos.com/rkt/stage1-fly:1.14.0 --inherit-env \
  --volume etc-fleet,kind=host,source=/etc/fleet \
  --volume machine-id,kind=host,source=/etc/machine-id \
  --volume dbus-socket,kind=host,source=/run/dbus/system_bus_socket \
  --volume fleet-units,kind=host,source=/run/fleet/units \
  ./fleetd-v0.12.0-amd64.aci

jonboulle/fleet,giantswarm/fleet,endocode/fleet,coreos/fleet,dongsupark/fleet,coreos/fleet,jonboulle/fleet,dongsupark/fleet,dongsupark/fleet,jonboulle/fleet,endocode/fleet,dalbani/fleet,endocode/fleet,giantswarm/fleet,dalbani/fleet,dalbani/fleet,coreos/fleet,giantswarm/fleet