oi-build package-install fails on already installed packages
If a component delivers two packages, and the first depends on the second, both get installed when the first is installed. When oi-build attempts to install the second, it fails with "no updates necessary for this image".
This has an exit code of 4, which gmake views as a failure, and believes the target has failed, when in fact it has succeeded.
I propose we ignore exit code 4.