builder/aws: Add pre validate step, to validate things before building.

Fixes 'unknown configuration key' errors for 'only' and 'except'

check the region before do the ami copy to fix the duplicate ami [GH-2123]

"Name" parameter required for copying ami across regions [GH-2172]

Fix a problem preventing `tag` or `save` from docker-tag artifacts

replace opscode with chef

Fix error in isotime demo in the documentation of Configuration Templates

Prevent select from spewing garbage to the terminal

Migrate to new AWS repo

Fail the build when go vet returns non-zero exit code

Support force option for docker-tag.

Interpolate the "push" config