Test cases may want to do call bitbake in setUpClass() but at that point the
previous selftest.inc is still present which could change the build
configuration and result in any built artifacts being removed in the next
bitbake invocation as part of the sysroot clean up.
Resolve this by cleaning selftest.inc in the tearDown, the clean in setUp should
be considered a safety net.
Signed-off-by: Ross Burton <ross.burton@intel.com>
