Rename cluster name to demo (#1000)

* Assign hostname to haproxy container
* Tune vim config

Dockerfile

@@ -37,6 +37,9 @@ RUN set -ex \
 \
     # haproxy dummy config
     && echo 'global\n        stats socket /run/haproxy/admin.sock mode 660 level admin' > /etc/haproxy/haproxy.cfg \
+\
+    # vim config
+    && echo 'syntax on\nfiletype plugin indent on\nset mouse-=a\nautocmd FileType yaml setlocal ts=2 sts=2 sw=2 expandtab' > /etc/vim/vimrc.local \
 \
     # Prepare postgres/patroni/haproxy environment
     && mkdir -p $PGHOME/.config/patroni /patroni /run/haproxy \