don't dex when installing an instant app

Bug: 38259387
Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.EphemeralTest
Test: install an instant app, see that it doesn't dex
Test: install a full app, see that it does dex
Change-Id: Id7dc749954d0be24bbd80da2ef0f43e39f77993e