build: fix issue with absolute path for OUTPUT_DIR

Before these changes, it was impossible to define a custom absolute
path for `OUTPUT_DIR` when calling the static-build/make_packages.sh
script. The build failed due to missing directory inside the container.
Also, set the default value for `OUTPUT_DIR` to the absolute path from
where the static-build/make_packages.sh script runs instead of relative
path to the static-build directory.

NO_DOC=build
NO_TEST=build
NO_CHANGELOG=build