It works!
\n\ ' > /usr/share/nginx/html/index.html RUN echo 'server {\n\ listen 80;\n\ server_name dummy-host.example.com;\n\ \n\ location / {\n\ root /usr/share/nginx/html;\n\ index index.html index.htm;\n\ add_header X-Location-echo $request_uri;\n\ add_header X-Default-VH 0;\n\ add_header Cache-Control "public, max-age=300";\n\ }\n\ \n\ # redirect server error pages to the static page /50x.html\n\ #\n\ error_page 500 502 503 504 /50x.html;\n\ location = /50x.html {\n\ root /usr/share/nginx/html;\n\ }\n\ }\n'> /etc/nginx/conf.d/vhost.conf