OF-1331 Warn user during setup when a session failure occurs

This is a complex problem.  During setup, fetching xmppSettings from the session may fail due to an invalid session state maintained between the client browser and the server.  This is likely caused by a previous HTTPS session to the same server hostname setting a `JSESSIONID` that subsequently can not be overwritten by the current HTTP openfire-setup session.

This introduces i18n string `setup.invalid_session`

src/i18n/openfire_i18n_en.properties

@@ -1848,6 +1848,7 @@ component.session.details.info=Below are details about the session with the exte
 # General Setup
 
 setup.title=Setup
+setup.invalid_session=A failure occurred while fetching your session from the server. This is typically a cookie issue.  Please either clear all cookies for this domain or try this URL again from an incognito browser session.
 
 # Setup environment check
 

src/web/setup/setup-profile-settings.jsp

@@ -23,6 +23,7 @@
     boolean scramOnly = JiveGlobals.getBooleanProperty("user.scramHashedPasswordOnly");
     boolean requestedScramOnly = (request.getParameter("scramOnly") != null);
     boolean next = request.getParameter("continue") != null;
+    boolean sessionFailure = false;
     if (next) {
         // Figure out where to send the user.
         String mode = request.getParameter("mode");
@@ -31,7 +32,9 @@
             // Set to default providers by deleting any existing values.
             @SuppressWarnings("unchecked")
             Map<String,String> xmppSettings = (Map<String,String>)session.getAttribute("xmppSettings");
-
+            if (xmppSettings == null){
+                sessionFailure = true;
+            } else {
                 xmppSettings.put("provider.auth.className", JiveGlobals.getXMLProperty("provider.auth.className",
                     org.jivesoftware.openfire.auth.DefaultAuthProvider.class.getName()));
                 xmppSettings.put("provider.user.className", JiveGlobals.getXMLProperty("provider.user.className",
@@ -54,6 +57,7 @@
                 response.sendRedirect("setup-admin-settings.jsp");
                 return;
             }
+        }
         else if ("ldap".equals(mode)) {
             response.sendRedirect("setup-ldap-server.jsp");
             return;
@@ -75,6 +79,12 @@
 	<fmt:message key="setup.profile.description" />
 	</p>
 
+<% if (sessionFailure) { %>
+            <span class="jive-error-text">
+            <fmt:message key="setup.invalid_session" />
+            </span>
+<% } %>
+
 	<!-- BEGIN jive-contentBox -->
 	<div class="jive-contentBox">
 	<form action="setup-profile-settings.jsp" name="profileform" method="post">