[util/cli] fix CLI invokation for sway

in sway/wayland, make sure that the wayland socket is cleared, which
seems to cause issue for some unspecified reason.

also, while at it, improve code so that the environment dict that is
passed in is *not* modified.

fixes #628

bumblebee_status/util/cli.py

@@ -33,14 +33,19 @@ def execute(
 
     if not env:
         env = os.environ.copy()
-    env["LC_ALL"] = "C"
+
+    myenv = env.copy()
+
+    myenv["LC_ALL"] = "C"
+    if "WAYLAND_SOCKET" in myenv:
+        del myenv["WAYLAND_SOCKET"]
 
     try:
         proc = subprocess.Popen(
             args,
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT if include_stderr else subprocess.PIPE,
-            env=env,
+            env=myenv,
             shell=shell,
         )
     except FileNotFoundError as e: