Display aci name + version after build

[MattKetmo]

Once the build is finished dgr should display the name + version of the built ACI (this would improve user experience especially when the version is dynamically generated via a template var).

It should work also for (clean) install/push.

[MattKetmo]

(Bonus) the output of dgr build should redirect to stderr while the display of the aci version at the end uses stdout (like the rkt prepare command which only outputs the pod uuid to stdout). So it would be easier to integrate it within a script (eg. ACI=$(dgr build))

[n0rad]

ACI=$(dgr build) is not doable because build include user printing stuff. but I can output the aci-name:version to a file in target/

[n0rad]

done in v73