Treat DIST_DIR and OUT_DIR as separate directories

If DIST_DIR is defined, create logs there and copy and
interesting artifacts to it.

The CI build (pKVM Busytown) expects build artifacts to be in
DIST_DIR. Previously the makefile would use the out directory for
that. However, this would clutter it with object files and
temporary build files that aren't needed.

Signed-off-by: Fuad Tabba <tabba@google.com>
Change-Id: I06669489553dbb4c1dc1900fb76701f12bc21ac0