ci: Update to the new west model

The new west is able to initialize itself from an existing zephyr clone
without modifying it, adapt the CI script accordingly.

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

scripts/ci/run_ci.sh

@@ -75,8 +75,8 @@ if [ -n "$MAIN_CI" ]; then
 
 	# West handling
         cd ..
-        west init .
-        west clone
+        west init -l zephyr
+        west update
         cd zephyr
 
 	if [ -z "$BRANCH" ]; then
@@ -89,11 +89,6 @@ if [ -n "$MAIN_CI" ]; then
 	source zephyr-env.sh
 	SANITYCHECK="${ZEPHYR_BASE}/scripts/sanitycheck"
 	if [ -n "$PULL_REQUEST_NR" ]; then
-		# west resets the tree after calling clone, so lets point back
-		# to the PR again.
-		git fetch origin pull/${PULL_REQUEST}/head
-		git checkout -f FETCH_HEAD
-		git merge -q origin/${PULL_REQUEST_BASE_BRANCH}
 		git rebase $REMOTE/${BRANCH};
 	fi
 fi