fixes #1340 - smtp server checks

Added new jQuery validation plugin rule of type pattern
Checks for smtp server to be valid (no spaces, no starting with -,
no chars !=digits or letters, all lowercase)

src/rockstor/storageadmin/static/storageadmin/js/views/email.js

@@ -96,7 +96,10 @@ EmailView = RockstorLayoutView.extend({
                 name: 'required',
                 sender: 'required',
                 password: 'required',
-                smtp_server: 'required',
+                smtp_server: {
+                    required: true,
+                    pattern: /^(([a-z\d]|[a-z\d][a-z\d\-]*[a-z\d])\.)*([a-z\d]|[a-z\d][a-z\d\-]*[a-z\d])$/
+                },
                 receiver: 'required',
                 username: {
                     required: "#enable_username:checked" //username field required only if username checkbox checked else empty
@@ -105,6 +108,11 @@ EmailView = RockstorLayoutView.extend({
                     number: true
                 }
             },
+            messages: {
+                smtp_server: {
+                    pattern: 'Please provide a correct hostname with only lowercase letters, digits and -'
+                }
+            },
 
             submitHandler: function() {
                 var button = $('#add-email');
@@ -246,4 +254,4 @@ EmailView = RockstorLayoutView.extend({
         });
 
     }
-});
+});