Bump Magnum Cluster API to 0.27.0

Add extra tool for bumping MCAPI by simply running:

> just bump-magnum-cluster-api

Change-Id: Ifbcc00b3012d14cbf2304390d999a8e425eeb6bb
diff --git a/images/magnum/Dockerfile b/images/magnum/Dockerfile
index a541211..eafa739 100644
--- a/images/magnum/Dockerfile
+++ b/images/magnum/Dockerfile
@@ -20,7 +20,7 @@
 pip3 install \
     --constraint /upper-constraints.txt \
         /src/magnum \
-        magnum-cluster-api==0.26.2
+        magnum-cluster-api==0.27.0
 EOF
 
 FROM openstack-python-runtime