MT#17727 Use http format for last-modified

Change-Id: I2291fe5ab4229594f48cd6ca15aae1f8b5be0176

lib/NGCP/Panel/Controller/Device.pm

@@ -16,6 +16,7 @@ use NGCP::Panel::Utils::Navigation;
 use NGCP::Panel::Utils::DeviceBootstrap;
 use NGCP::Panel::Utils::Device;
 use NGCP::Panel::Utils::DateTime;
+use DateTime::Format::HTTP;
 
 BEGIN { use base 'Catalyst::Controller'; }
 
@@ -1162,7 +1163,7 @@ sub dev_field_config :Chained('/') :PathPart('device/autoprov/config') :Args() {
     delete $c->response->cookies->{ngcp_panel_session};
     $c->response->headers->remove_header('Connection');
     $c->response->headers->remove_header('X-Catalyst');
-    $c->response->headers->push_header('Last-Modified' => NGCP::Panel::Utils::DateTime::current_local);
+    $c->response->headers->push_header('Last-Modified' => DateTime::Format::HTTP->format_datetime());
 
     # this is going to be used if we want to do the cert check on the server,
     # the format is like this:
@@ -1422,7 +1423,7 @@ sub dev_field_bootstrap :Chained('/') :PathPart('device/autoprov/bootstrap') :Ar
     delete $c->response->cookies->{ngcp_panel_session};
     $c->response->headers->remove_header('Connection');
     $c->response->headers->remove_header('X-Catalyst');
-    $c->response->headers->push_header('Last-Modified' => NGCP::Panel::Utils::DateTime::current_local);
+    $c->response->headers->push_header('Last-Modified' => DateTime::Format::HTTP->format_datetime());
 
 
     foreach my $did (@id) {