Artifacts listing funcs in workspace
Artifacts listing funcs in workspace

This commit adds three functions to workspace.go to get the
artifacts produced for a given version:

ListBuildImages: Returns a list if the image archives
ListBuildTarballs: Returns the various tarballs before staging
ListBuildBinaries: Returns a struct of binaries, organized by arch and platform

Signed-off-by: Adolfo García Veytia (Puerco) <9de42c8261a7cacaae239656a4dd6991d9b9250f@uservers.net>

kubernetes/release,kubernetes/release