Fix bug where RollbackManagerService ignores package name.

RollbackManagerService incorrectly ignores the package name passed to
getAvailableRollback and executeRollback.

This CL fixes the bug and adds a regression test. The infrastructure for
having multiple test apps in RollbackTest will also be useful for
testing rollback of multi-package installs.

Test: atest RollbackTest (with selinux disabled)
Bug: 112431924

Change-Id: I84c8fdeb97aba557a1f8fd2e71a2bb0d87b10636