Have test-art-host-dexdump specifically depend on the host binaries.

dexdump2 and dexlist2 are phony targets representing both the host and
target binaries.
Also set environmental variable ANDROID_HOST_OUT=$(realpath $(HOST_OUT))
before calling art/test/dexdump/run-all-tests.
art/test/dexdump/run-all-tests references ANDROID_HOST_OUT, which may be
not set up by the user if he didn't run build/envsetup.sh.

Bug: 22343844
Change-Id: I38b5f3efccd5817d7d9ff0e91b5c6d070b546d77