exec_python stuff like in bind10.in

git-svn-id: svn://bind10.isc.org/svn/bind10/branches/f2f200910@263 e5f2f494-b856-4b98-b285-d166d9295462

src/bin/bind-cfgd/bind-cfgd.in

@@ -3,5 +3,7 @@
 BINPATH=@abs_top_srcdir@/src/lib/bind-cfgd/python
 LIBPATH=@abs_top_srcdir@/src/lib/cc/python
 
-PYTHONPATH=${LIBPATH}:${PYTHONPATH} python3 ${BINPATH}/bind-cfgd.py
+PYTHON_EXEC=${PYTHON_EXEC:-/usr/bin/python3.0}
+
+PYTHONPATH=${LIBPATH}:${PYTHONPATH} ${PYTHON_EXEC} ${BINPATH}/bind-cfgd.py