Dependency artifacts are missing from storage even when they are required

We have cases when for some reason artifacts gets lost from storage, even if those are required for building. For example:
https://testresults.qt.io/coin/integration/pyside/pyside-setup/tasks/1512314942

No binary artifacts for "/home/vmbuilder/ci-working-dir/storage/qt/qtbase/209bb9b26db15b6673003cac1ff8fa69c5886215/LinuxRHEL_6_6x86_64LinuxRHEL_6_6x86_64GCCqtci-linux-RHEL-6.6-x86_64-a4584eRelease_NoUseGoldLinker/2a48a3b7dcb9652b1532a3ad14de7580b5b9b1ee/build_1506108045/artifacts.tar.gz" skipping

details in:
https://testresults.qt.io/logs/pyside/pyside-setup/f1c8b5ee5de685590a5a9d8cdd526959d03952b0/LinuxRHEL_6_6x86_64LinuxRHEL_6_6x86_64GCCqtci-linux-RHEL-6.6-x86_64-a4584eRelease_NoUseGoldLinker/ac8cc81debc09de4f89f98336dbf6f548b7af908/build_1512314950/log.txt.gz

Instead of just skipping the extraction, we should build the missing artifacts. While this is not done, there is no way to re-create the missing files, except manually deleting build_success files from storage. That can be quite laborious task especially if all qt5 artifacts from all configurations are missing.