Build OPC-UA server.

slapos/software/osie-coupler/software-c.cfg

 [buildout] 
 parts = 
   open62541
-  osie-repository
-#  compile-coupler
+  compile-coupler
 
 extends =   
   https://lab.nexedi.com/nexedi/slapos/raw/master/stack/slapos.cfg
@@ -45,4 +44,6 @@ location = ${buildout:parts-directory}/osie
 
 [compile-coupler]
 recipe = slapos.recipe.cmmi
-path = ${open62541:location}
+path = ${osie-repository:location}/coupler/opc-ua-server/
+environment =
+  OPEN62541_HOME = ${open62541:location}/build