Use tempfiles for clircle tests

Cargo.toml

@@ -79,6 +79,9 @@ predicates = "1.0.7"
 wait-timeout = "0.2.0"
 tempfile = "3.2.0"
 
+[target.'cfg(unix)'.dev-dependencies]
+nix = "0.19.1"
+
 [build-dependencies]
 clap = { version = "2.33", optional = true }