Refactor libinit_test_utils to not use libinit and expose its libraries

Users of libinit_test_utils must include all libraries that it uses.
If it uses libinit, then there is a large number of libraries that
must be included.  To avoid this, make libinit_test_utils only use
init_common_sources and the small number of required libraries that go
along with those sources.  Additionally, expose these sources as a
default for users of libinit_test_utils.

Test: build
Change-Id: I224fa7e0590d073e4cd40412b5dcb6f72a64b6bf