Finish package installer activity on a cancel result

We made a change to the PackageInstaller to start settings for
a result to allow partners to return OK to continue the install
flow, otherwise requiring the user to start install again (the
desired behavior on Nexus). This change finishes the package
installer activity if settings does not return success to
continue the install flow.

bug:28838075

Change-Id: I4ff1b1a713d46a8584baf66f379ab070226c125f