Add quotes around url_prefix

When url_prefix is set to '', it becomes converted into None
instead of empty string. To fix this, add quotes around it.

Change-Id: I400b7ebf1b5021d14a50187091cd3955355e07e5
Related-prod: #PROD-27934 (PROD:27934)
diff --git a/.kitchen.yml b/.kitchen.yml
index 8fd1b87..3afbc72 100644
--- a/.kitchen.yml
+++ b/.kitchen.yml
@@ -37,16 +37,10 @@
   sudo: true
 
 docker_images:
-  - &xenial-20163 <%=ENV['IMAGE_XENIAL_20163'] || 'docker-dev-local.docker.mirantis.net/epcim/salt/saltstack-ubuntu-xenial-salt-2016.3/salt:2018_11_19'%>
   - &xenial-20177 <%=ENV['IMAGE_XENIAL_20177'] || 'docker-dev-local.docker.mirantis.net/epcim/salt/saltstack-ubuntu-xenial-salt-2017.7/salt:2018_11_19'%>
   - &xenial-stable <%=ENV['IMAGE_XENIAL_STABLE'] || 'docker-dev-local.docker.mirantis.net/epcim/salt/saltstack-ubuntu-xenial-salt-stable/salt:2018_11_19'%>
 
 platforms:
-  - name: xenial-2016.3
-    driver_config:
-      image: *xenial-20163
-      platform: ubuntu
-
   - name: xenial-2017.7
     driver_config:
       image: *xenial-20177
diff --git a/gerrit/meta/salt.yml b/gerrit/meta/salt.yml
index bb80871..2a1dc4e 100644
--- a/gerrit/meta/salt.yml
+++ b/gerrit/meta/salt.yml
@@ -13,7 +13,7 @@
       http_port: {{ client.server.http_port }}
       {%- endif %}
       {%- if client.server.url_prefix is defined %}
-      url_prefix: {{ client.server.url_prefix }}
+      url_prefix: "{{ client.server.url_prefix }}"
       {%- endif %}
       {%- if client.server.password is defined %}
       password: {{ client.server.password }}