APEX respects relative_install_path

relative_install_path for cc_library is respected by APEX.

relative_install_path for cc_binary is not yet respected because doing
it will break the path to the dynamic linker in the runtime APEX.
That change should be done along with changes in init, bionic, etc.

Bug: 123721777
Test: m (apex_test.go amended)
Change-Id: I855f8eda0d4255d563861ac96d0d3e2c669e9a2a