scripts: build ACI image using acbuild

[dongsupark]

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 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 \
   --volume etc-fleet,kind=host,source=/etc/fleet \
   ./fleetd-v0.12.0-amd64.aci