bundlebuilder: install: add destdir support
bundlebuilder: install: add destdir support

Add support for DESTDIR using a --destdir option,
https://www.gnu.org/prep/standards/html_node/DESTDIR.html

Fixes https://github.com/sugarlabs/sugar-toolkit-gtk3/issues/453

Fixes https://bugs.debian.org/975373

Fixes https://bugs.debian.org/975374

sugarlabs/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3