landing-preview: add a shim to display blockers dryrun info if available (Bug 1888188) (#198)

As part of the checks refactor we will eventually support displaying
multiple blockers in the front end. Add a shim so Lando-UI can handle
output from before and after the refactor PR in LandoAPI is landed
and deployed.

Author: cgsheeh

landoui/templates/stack/partials/landing-preview.html

@@ -9,10 +9,11 @@ <h3 class="StackPage-landingPreview-sectionLabel">Landing is Blocked</h3>
   <div class="StackPage-landingPreview-section StackPage-landingPreview-blocker">
     Reason for blockage is unknown
   </div>
-{% elif dryrun['blocker'] %}
+{% elif dryrun['blocker'] or dryrun['blockers'] %}
+  {% set blocker = dryrun['blockers'][0] if 'blockers' in dryrun else dryrun['blocker'] %}
   <h3 class="StackPage-landingPreview-sectionLabel">Landing is Blocked</h3>
   <div class="StackPage-landingPreview-section StackPage-landingPreview-blocker">
-    {{ dryrun['blocker']|escape_html|linkify_faq|safe }}
+    {{ blocker|escape_html|linkify_faq|safe }}
   </div>
 {% elif series %}
   <h3 class="StackPage-landingPreview-sectionLabel">

landoui/templates/stack/partials/revision-status.html

@@ -4,7 +4,8 @@
     file, You can obtain one at https://mozilla.org/MPL/2.0/.
 #}
 
-{% if revision['blocked_reason'] %}
+{% if revision['blocked_reasons'] or revision['blocked_reason'] %}
+{% set blocked_reason = revision['blocked_reasons'][0] if 'blocked_reasons' in revision else revision['blocked_reason']%}
 <div class="StackPage-blockerReason">
   <div class="Badge Badge--negative">
     Blocked