doctor: check for 'cipd' in PATH.

Also add the cipd installation folder to PATH.

Change-Id: I871b466079250473c41adcba61bd8787305c795f
diff --git a/env_setup/cipd/update.py b/env_setup/cipd/update.py
index 53ba1aa..530be74 100755
--- a/env_setup/cipd/update.py
+++ b/env_setup/cipd/update.py
@@ -89,7 +89,7 @@
     if not os.path.isdir(args.install_dir):
         os.makedirs(args.install_dir)
 
-    paths = []
+    paths = [args.install_dir]
     env = {
         'CIPD_INSTALL_DIR': args.install_dir,
         'CIPD_CACHE_DIR': args.cache_dir,
diff --git a/pw_doctor/py/pw_doctor/doctor.py b/pw_doctor/py/pw_doctor/doctor.py
index 266352b..d0a0c48 100755
--- a/pw_doctor/py/pw_doctor/doctor.py
+++ b/pw_doctor/py/pw_doctor/doctor.py
@@ -109,6 +109,10 @@
     """Check cipd is set up correctly and in use."""
     cipd_path = 'pigweed'
 
+    cipd_exe = shutil.which('cipd')
+    if not cipd_exe:
+        ctx.fatal('cipd not in PATH')
+
     temp = tempfile.NamedTemporaryFile(prefix='cipd', delete=False)
     subprocess.run(['cipd', 'acl-check', '-json-output', temp.name, cipd_path],
                    stdout=subprocess.PIPE)