Add timing to the build goal

[davsclaus]

When building a docker image, then a lot of time can be spent in

• pulling images
• building the .tar

I would like if the d-m-p could report how long time that task took in seconds.

[INFO] - Pulling images took 49 seconds
[INFO] - Building tar took 37 seconds

And I guess there is also timing for a docker:push could be good to have as well.

[andyshinn]

This would be very helpful. Good idea!

[jgangemi]

this shouldn't be too difficult, i'll see about getting this done along side some other things i'm doing.