linker_config_test: allow search paths of systems without a vendor partition

linker_config#smoke and linker_config.asan_smoke are trying to find
paths under the /vendor directory. If there is no vendor partition,
the real path of them is started with /system/vendor.

This CL allows those paths in the tests by getting the resolved paths
for systems without a vendor partition.

Bug: http://b/62562515
Test: linker_config_test passes without a vendor partition.
Change-Id: Id6d16ef623efd81ab9083c3e819da2ad22a28bf8