Make cipd auth-login issue more clear

Don't print lots of other output if CIPD auth fails.

Fixed: 132
Change-Id: I3a497083068bb74cb63a7ace86ec74440375310e

pw_env_setup/py/pw_env_setup/virtualenv_setup/install.py

diff --git a/pw_env_setup/py/pw_env_setup/virtualenv_setup/install.py b/pw_env_setup/py/pw_env_setup/virtualenv_setup/install.py
index c861369..b0f2a16 100644
--- a/pw_env_setup/py/pw_env_setup/virtualenv_setup/install.py
+++ b/pw_env_setup/py/pw_env_setup/virtualenv_setup/install.py
@@ -85,6 +85,14 @@
 ):
     """Creates a venv and installs all packages in this Git repo."""
 
+    version = subprocess.check_output(
+        (python, '--version'), stderr=subprocess.STDOUT).strip().decode()
+    if '3.8' not in version:
+        print('=' * 60, file=sys.stderr)
+        print('Unexpected Python version:', version, file=sys.stderr)
+        print('=' * 60, file=sys.stderr)
+        return
+
     pyvenv_cfg = os.path.join(venv_path, 'pyvenv.cfg')
     if full_envsetup or not os.path.exists(pyvenv_cfg):
         print('Creating venv at', venv_path)