Add an empty .so to CTS for testing multiArch upgrade
Pre-built apk will be updated separately after this is merged
Testing build command will be updated later
Bug: 64504762
Test: all related cts and gts pass
Test: pre-built passed on all arch, including x86_64
Test: gts-tradefed run commandAndExit gts-dev --module GtsPackageManagerHostTestCases
Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.PrivilegedUpdateTests
Change-Id: I5abfe06de0bd730b5cdc317df344b7567d50aff6
