Fix multi-image boot class path construction.

This changes the stored boot class path components of the
boot image prebuilts to exclude the bogus
    out/target/product/taimen/dex_bootjars/system/framework/
part and leaves only
    /system/framework/boot*.art
but it does not impact the loading of the boot image at all.

Also remove the "infix" from core image filenames as it was
duplicating a part of the prefix, thus
    core-interp-ac-core-libart-interp-ac.art
shall change to
    core-interp-ac-core-libart.art

Test: Manual inspection of "m dump-oat-boot" output.
Test: m test-art-host-gtest
Test: testrunner.py --host
Change-Id: Iffbab30be8b8ce6f8f2aec8985e94177db517653