Limit stage install to system and whitelisted packges only (2/2)

Add a whitelist check to limit staged installers beside system and a pm
shell command to bypass the next staged installer check.

Bug: 148664742
Test: atest StagedInstallerTest StagedRollbackTest
Change-Id: Ie9297ad8c1b74c2e63a08c71f2279658661f9a32