Do not use a sandbox when not required for checkout
Description
Even tho a sandbox is not required when we checkout without integration eg.
bst -o target_board rpi3 -o target_arch aarch64 artifact checkout --no-integrate deploy/image.bst
A sandbox is still setup which means that while bst can pull a artefact from a different architecture the artefact can not be checked out.
Proposed changes
The key code path is stage_dependency_artifacts
which takes a sandbox but then only uses the vdir from that sandbox. by changing this function to take only the vdir then it can be called without a sandbox and we can then checkout artefacts without needing the sandbox.
Edited by William Salmon