Don't abort multi-package install early

The multi-package install flow depends upon all of the packages being
processed. If we ever skip one, any installation status will never be
returned to the installation observer.

Fixes: 134632533
Test: adb install-multi-package app1/base.apk app2/base.apk app3/base.apk app4/base.apk
Test: adb did not hang and returned proper error "Failure [INSTALL_FAILED_VERSION_DOWNGRADE"
Change-Id: I3c0d1df059e1411c2d77f96b8fb656c9d1050ce1