Recent enhancements in the installer are costly. We need to improve it.

One slow place is image preparation (mostly because of signing)
signing is not instant, especially when network is flaky and we repeat work for both runtime and SDK installers

I think it make sense to restructure build to be:
    a) shared step to prepare signed image that is superset of SDK and rt
    b) both runtime and installer will just copy it files they need from there