Refactor image loading.

Try to load all boot class path components from the same
place (system or dalvik cache) instead of looking for each
component image file separately.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: If5d9f39c6ec21d9be05fe36a42c70224d6fef27a
3 files changed