tests: add ids to elements for testing automation

web/templates/password.html

@@ -17,12 +17,12 @@
     </div>
 
     {{ if .Invalid }}
-      <div class="dex-error-box">
+      <div id="login-error" class="dex-error-box">
         Invalid username and password.
       </div>
     {{ end }}
 
-    <button tabindex="3" type="submit" class="dex-btn theme-btn--primary">Login</button>
+    <button tabindex="3" id="submit-login" type="submit" class="dex-btn theme-btn--primary">Login</button>
 
   </form>
 </div>