Prevent using android_app_import in instrumentation_for property

Previously, referencing a prebuilt android_app_import in an
android_test's instrumentation_for property instead of the source
android_app module (e.g. because the prebuilt is preferred) could
result in compilation errors if the android_test sources depended on
classes from the app. That is because while the android_app provides a
classes jar file to be added to the android_test's classpath the
android_app_import does not.

This change reports that situation as an error.

Bug: 207128192
Test: m nothing
Change-Id: I26ea90e7a3f57707fc0c094e0d8b8dc9a9e135ac