fetch_cargo_deps.py: ensure CARGO_HOME is used (#1804)

This PR ensures that CARGO_HOME is used (rather than the default of ~/.cargo) when fetching cargo deps, and also gets rid of the llnl.* deprecation warning for fetch_cargo_deps.py.

Author: AlexanderRichert-NOAA

util/fetch_cargo_deps.py

@@ -25,7 +25,7 @@
 from spack_repo.builtin.build_systems.python import PythonPackage
 from spack.package_base import PackageBase
 from spack.util.executable import Executable, which
-from llnl.util.filesystem import working_dir
+from spack.llnl.util.filesystem import working_dir
 from spack.store import find
 from spack.util.environment import EnvironmentModifications
 from spack.error import SpackError
@@ -117,6 +117,7 @@
         cargo_exe = Executable(cargo_wrapper)
 
     env = EnvironmentModifications()
+    env.set("CARGO_HOME", cargo_home)
     if cargo_bin:
         env.prepend_path("PATH", cargo_bin)
     for root, dirs, files in os.walk(pkg.stage.source_path):