[New: openFATE 309363] Support offline build with "osc build"

Feature added by: Adrian Schröter (adrianSuSE) Feature #309363, revision 1 Title: Support offline build with "osc build" Buildservice: Done Priority Requester: Important Requested by: Adrian Schröter (adriansuse) Description: osc build --preload is loading needed packages to support osc build --offline with entire network less setup of build system. This works as long as no build dependencies are changing. -- openSUSE Feature: https://features.opensuse.org/309363