catkin.bbclass: Use out of tree build

Build catkin packages out of tree as this is the default of ros and
makes it simple to identify build paths.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

classes/catkin.bbclass

@@ -22,6 +22,9 @@ EXTRA_OECMAKE_prepend = "\
     -DSETUPTOOLS_DEB_LAYOUT=OFF \
     "
 
+OECMAKE_SOURCEPATH = "${S}"
+OECMAKE_BUILDPATH = "${S}/build"
+
 export BUILD_SYS
 export HOST_SYS