dex2oat_vdex_test: add missing dependency on core boot image.

Bug: 178055795

Test: lunch armv8 \
  && rm out/host/linux-x86/framework/x86_64/core.art \
  ; m SOONG_ALLOW_MISSING_DEPENDENCIES=true \
    test-art-host-gtest-dex2oat_vdex_test64
  # failed before this CL, now passes

Change-Id: I2bc5dde0916393842cd444d256022c9b1c36343b
Merged-In: I5b104329af899ea62dc1779800264bad6b5424a4
(cherry picked from commit c60638a44e3d0b78b704665650d58044cf0195e3)