A handful of the std::filesystem tests assume non-root (such as
checking readability of a file that has mode 000). We probably
shouldn't be running as root for these tests anyway.
Test: ./run_tests.py --bitness 32
Test: ./run_tests.py --bitness 64
Bug: None
Change-Id: Ifc661bd245c3d802d8816d1c098b0e47d011c4fa