Deterministic staging

Description

This MR fixes a bunch of issues related to determinism of file attributes from source plugins.

• Running bst with a different umask should not change the permission of the extracted files.
• Whether bst is run as root or as an unprivileged user, should not change file attributes of files extracted by tar.
• local plugin used with files extracted should always have the same attributes, including permissions. This no matter how the sources of the project were extracted (git, tar ball, etc.)

Changes

• local plugin now uses only 0755 or 0644 rights for files.
• bzr, git, and patch are run with 0022 umask.
• We fix permissions on files extracted by zip.
• tar ignores users.

Issues

This merge request, when approved, will close issue/bug: #527 (closed) #540 (closed) #541 (closed) #542 (closed) #543 (closed) #545 (closed)

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