buildpackage: remove export_dir if build fails

Previously, the export_dir was not removed if the build command (set by --git-builder) failed, or was interrupted.

This commit ensures it is removed, unless --git-no-purge is used

Not removing is useful for debugging, but does not need to be the default

Closes: #1088179

added 3 commits

• fecf834f...22fb2c54 - 2 commits from branch agx:master
• c9cc8df4 - buildpackage: remove export_dir if build fails

Compare with previous version

enabled an automatic merge when all merge checks for c9cc8df4 pass

Thanks!

mentioned in commit f47792ec

merged