executor: don't consider failures to remove temp dirs as crashes
executor: don't consider failures to remove temp dirs as crashes

There is a number of known, low-frequency reasons for failures in remove_dir.
Make the failures non-fatal.

Fixes #45

xairy/syzkaller,zoulasc/syzkaller,hyz0906/syzkaller,xairy/syzkaller,dotweiba/syzkaller,google/syzkaller,hyz0906/syzkaller,xairy/syzkaller,xairy/syzkaller,hyz0906/syzkaller,xairy/syzkaller,sploving/syzkaller,google/syzkaller,google/syzkaller,sploving/syzkaller,google/syzkaller,zoulasc/syzkaller,dotweiba/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,hyz0906/syzkaller,sploving/syzkaller,dotweiba/syzkaller,dotweiba/syzkaller,sploving/syzkaller,google/syzkaller,zoulasc/syzkaller,zoulasc/syzkaller,hyz0906/syzkaller