out-of-tree build: generate ./run from template, fix image checks

out-of-tree build: generate ./run from template, fix image checks

./run can now be run in a separate build directory. Since some files
needed in the image checks are found in the source tree (but not the
build tree), the source tree location is passed to make-*-img.sh via
an environment variable.
(cherry picked from commit 70c033998e0e721dc4f9eb2a20348098b259752c)