Metadata: add hostname to the available metadata options

Having the hostname allows us to identify which machine rendered which
frame in our render farm.

This simply uses the host's name, and doesn't do any DNS lookup of any
IP address of the machine. As such, it's only usable for identification
purposes, and not for reachability over a network.

Reviewers: sergey, brecht

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D4047

release/scripts/startup/bl_ui/properties_output.py

@@ -205,6 +205,8 @@ class RENDER_PT_stamp(RenderOutputButtonsPanel, Panel):
         col.prop(rd, "use_stamp_frame_range", text="Frame Range")
         col = flow.column()
         col.prop(rd, "use_stamp_memory", text="Memory")
+        col = flow.column()
+        col.prop(rd, "use_stamp_hostname", text="Hostname")
 
         col = flow.column()
         col.prop(rd, "use_stamp_camera", text="Camera")