Test dex jar paths provided to apex by bootclasspath_fragment

This change adds a test to verify the existing behavior to provide a
baseline against which following changes can be compared.

Bug: 179354495
Test: m nothing
Merged-In: Ib7dadf3e65151f4e925251f7b1a9c099e824ea63
Change-Id: Ib7dadf3e65151f4e925251f7b1a9c099e824ea63
(cherry picked from commit f2fa0b5e)