fix to pass os::tests::copy_file_ok on android

[yichoi]

To enable test on android bot #9120

libstd/rt/io/fs.rs :
fn copy_file_ok() {
...
}

this issue depends #10175

[alexcrichton]

This test no longer exists in os, but rather in fs. What's the error that you're seeing when running the test?

[yichoi]

seems not reproduced any more. closing