Extract verification of version code into a separate method

Overriding install location is required for installation of package.
Verification of version code of package is required for package
verification. Keeping them separate make it easier to split verifcation
phase from install phase in future.

Bug: 136257624
Test: atest StagedInstallTest
Test: atest AtomicInstallTests
Test: atest GtsSecurityHostTests
Change-Id: I42b05d5cab86b4c14e7649b337dc997e0c8ee55f