Refactor ci helper functions

Signed-off-by: Andrei Dinin <adinin@pivotal.io>
Refactor promote and publish boxes

Signed-off-by: Andrei Dinin <adinin@pivotal.io>
Move download and upload box to ci_helpers

Signed-off-by: Andrei Dinin <adinin@pivotal.io>
Upload local boxes to bucket after building

Signed-off-by: Andrei Dinin <adinin@pivotal.io>