build,ib: add STRIP_ABI option for manifest

build,ib: add STRIP_ABI option for manifest

The ImageBuilder `make manifest` prints all installed packages. This
function can be used to create a list of package and corresponding
package versions before attempting image creation.

When called with `--strip-abi` OPKG can automatically strip attached
ABIVersions from package names. Make this function accessible for the
ImageBuilder by adding a `STRIP_ABI` variable.

Signed-off-by: Paul Spooren <mail@aparcar.org>
(cherry picked from commit 0f7cd97f812adaf4b2c2048227610d150aec72cc)