[LTI Provider] Made reverifications parameter to courseware optional

lms/templates/dashboard/_dashboard_prompt_midcourse_reverify.html

 <%! from django.utils.translation import ugettext as _ %>
 <%! from django.core.urlresolvers import reverse %>
-% if reverifications["must_reverify"]:
+
+% if reverifications:
+    % if reverifications["must_reverify"]:
       % if len(reverifications["must_reverify"]) > 1:
 
       <div class="wrapper-msg urgency-high">
@@ -57,10 +59,10 @@
         </div>
       % endfor
       %endif
-%endif
+    %endif
 
-%if reverifications["denied"] and denied_banner:
-<div class="wrapper-msg urgency-high" id="failed-verification-banner">
+    %if reverifications["denied"] and denied_banner:
+    <div class="wrapper-msg urgency-high" id="failed-verification-banner">
       <div class="msg msg-reverify is-dismissable">
           <div class="msg-content">
             <h2 class="title">${_("Your re-verification failed")}</h2>
@@ -84,4 +86,5 @@
           </div>
         </div>
       </div>
+    %endif
 %endif