Silence PRODUCT_COPY_FILES ignored messages

We don't have great alternatives for some of these use cases, so for now
just silence them, writing them to $OUT/product_copy_files_ignored.txt
(and if `dist' is specified, $DIST_DIR/logs/product_copy_files_ignored.txt)

Test: lunch aosp_arm-userdebug; m nothing
Test: lunch aosp_arm-userdebug; m dist
Change-Id: If0228bc8d907346e3505ae136cb477ef37a5c867