"cargo clean" puts lock on package cache

[matthiaskrgr]

Problem
cargo clean puts a lock on the package cache (cargo home) but I think it should not need it at all?

Steps

1. Have cargo fetch of some git repo run on project 1.
2. Try to cargo clean a different repo at the same time
   =>
   Blocking waiting for file lock on package cache

Possible Solution(s)
I don't really see why we need to take the $CARGO_HOME lock into account here, after all we only need to rm -rf target..?

Notes

Output of cargo version:
cargo 1.40.0-nightly (8b0561d68 2019-09-30)

[ehuss]

I think it would be fine to move this line below line 63 if you want to fix this.

[matthiaskrgr]

Thanks!