Stop creating extra apk session during pre-reboot verification

Now that verification logic has been separated out from install flow, we
can reuse the original session for apk verification without depending on
extra session with dry run flag.

Apex sessions are also allowed to follow along but they are ignored in
the verification process for now.

Unused codes will be removed in follow up cls.

Bug: 159336213
Test: atest StagedInstallTest
Test: atest GtsSecurityHostTestCases
Test: atest CtsAtomicInstallTestCases
Change-Id: I8b0511a6af4360253595bacc6c9f72da81920246