Currently the autobuilder saves failed build directories. This doesn't work for oe-selftest since it deletes all build directories when it completes. Add a mode to selftest where it would leave the directories for failed builds behind to allow for later debugging of otherwise hard to understand failures.
Build directory deletion is this code: http://git.yoctoproject.org/cgit.cgi/poky/tree/meta/lib/oeqa/core/utils/concurrencytest.py#n294 (see removebuilddir)
Fixed: https://git.openembedded.org/openembedded-core/commit/?id=3d5aa170d2e88b852bd2a4452aab9311a24badef