Fix SQLiteLibraryLoader tests

Fixes build failure: https://travis-ci.org/robolectric/robolectric/builds/15288333.

Don't invoke real loading for fake environments, just check paths used for picking a library.

Seems like tests did not fail before due to a bit of luck with tests execution order: real loading test (`shouldExtractNativeLibrary` e.g.) was invoked first, so that calls to `doLoad()` in tests with fake environments were ignored since the library had already been loaded.