While at it, we should correct this code and use the effective deps dir which may not necessarily be the default "deps".
So, how about exporting `rebar_deps:get_deps_dir/1` for internal use only by adding it [here](https://github.com/rebar/rebar/blob/620c4b01c/src/rebar_deps.erl#L42) and reusing it in `rebar_ct:collect_files/2`? There may be other files where we should reuse `get_deps_dir/1` for correctness.