pw_env_setup: hide rust step

Change-Id: I5599550cf8c5b6f68d22d3ec3d91af6a0612808d

pw_env_setup/py/pw_env_setup/env_setup.py

diff --git a/pw_env_setup/py/pw_env_setup/env_setup.py b/pw_env_setup/py/pw_env_setup/env_setup.py
index 67f653b..6472caa 100755
--- a/pw_env_setup/py/pw_env_setup/env_setup.py
+++ b/pw_env_setup/py/pw_env_setup/env_setup.py
@@ -213,7 +213,7 @@
         ]
 
         # TODO(pwbug/63): Add a Windows version of cargo to CIPD.
-        if not self._is_windows:
+        if not self._is_windows and os.environ.get('PW_CARGO_SETUP', ''):
             steps.append(("Rust cargo", self.cargo))
 
         self._log(