fix zendesk not getting the right user on new tickets

In the old form, the form would post a blank
report[email] value.  because of the way
guess_email works we can't just not submit it. 
because it needs to override the "unknown" value 
that was put there in the after_save callback when
it was created (but did not yet have an associated
user)

test_plan:
 * run the spec 
Manual steps:
 * in an environment with the canvas_zendesk_plugin
   set up, submit something a problem from the 
   help dialog
 * make sure the ticket in zendesk has the right
   email address.

Change-Id: I23d983da41e154815c7f28fe64fb70f03a0a9803
fixes: #7018
Reviewed-on: https://gerrit.instructure.com/8255
Reviewed-by: Jon Jensen <jon@instructure.com>
Tested-by: Hudson <hudson@instructure.com>

app/views/jst/helpDialog.handlebars

@@ -56,10 +56,10 @@
       <option value="blocks_what_i_need_to_do">{{#t "i_cant_get_things_done_until_i_hear_back_from_you"}}I can't get things done until I hear back from you{{/t}}</option>
       <option value="extreme_critical_emergency">{{#t "extreme_critical_emergency"}}EXTREME CRITICAL EMERGENCY!!{{/t}}</option>
     </select>
-    {{#if showEmail}}
+    <div style="{{hiddenUnless showEmail}}">
       <label for="error-email">{{#t "your_email_address"}}Your email address{{/t}}</label>
       <input type="email" name="error[email]" id="error-email">
-    {{/if}}
+    </div>
     <div class="button-container">
       <button type="submit" data-text-while-loading="{{#t "Submitting_Ticket"}}Submitting Ticket...{{/t}}" class="button submit_button"><img src="/images/email.png" alt=""/>{{#t "submit_this_support_request"}}Submit Ticket{{/t}}</button>
     </div>

spec/selenium/help_dialog_spec.rb

@@ -114,6 +114,7 @@ describe "help dialog" do
     er.subject.should == 'test subject'
     er.comments.should == 'test comments'
     er.data['user_perceived_severity'].should == severity
+    er.guess_email.should eql @user.email
   end
 
   it "should not show the 'Message teacher' button if not a student" do