Allow override of TMPDIR, IMAGE_DEPLOY_DIR and more
Allow override of TMPDIR, IMAGE_DEPLOY_DIR and more

Change to weak assignment, allowing override of a number of basic dir
variables using ENV variables.

Signed-off-by: Esben Haabendal <da90c138e4a9573086862393cde34fa33d74f6e5@haabendal.dk>

sknsean/core,sknsean/core,sknsean/core,sknsean/core,sknsean/core