Suppress welcome message in 'py list -1' output. (#208)

Also moves it to standard error instead of stdout.
Fixes #203

Author: zooba

src/manage/commands.py

@@ -516,7 +516,7 @@ def show_welcome(self, copyright=True):
         except OSError:
             LOGGER.debug("Failed to update %s", last_update_file, exc_info=True)
             return
-        LOGGER.print(WELCOME)
+        LOGGER.info(WELCOME)
 
     def dump_arguments(self):
         try:
@@ -716,7 +716,10 @@ class ListCommand(BaseCommand):
 
     def execute(self):
         from .list_command import execute
-        self.show_welcome()
+        # gh-203: Don't show welcome message for "-1" to minimise the risk of it
+        # mixing with parsed output.
+        if not self.one:
+            self.show_welcome()
         if self.default_source:
             LOGGER.debug("Loading 'install' command to get source")
             inst_cmd = COMMANDS["install"](["install"], self.root)