west: Add completion command

Add a completion command that dumps the contents of a shell
completion file present in the zephyr repository.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>

scripts/west-commands.yml

diff --git a/scripts/west-commands.yml b/scripts/west-commands.yml
index 807489b..81ff630 100644
--- a/scripts/west-commands.yml
+++ b/scripts/west-commands.yml
@@ -1,5 +1,10 @@
 # Keep the help strings in sync with the values in the .py files!
 west-commands:
+  - file: scripts/west_commands/completion.py
+    commands:
+      - name: completion
+        class: Completion
+        help: display shell completion scripts
   - file: scripts/west_commands/boards.py
     commands:
       - name: boards