Add tests for multiton issue

Test accessing a singleton from two libraries, the second of which
depends on the first but is dlopen'd after the first is already
loaded.

Bug: 35674422
Test: out/host/linux-x86/nativetest64/libutils_tests/libutils_tests
Change-Id: I975ba933a19b941a52bdb6e9c221a6910ffb8081