component/macros/virtual-env: Create a default instance

Now, `virtual-env.cfg` will create an instance by default.

This instance will publish `activate` script path.

component/macros/virtual-env.cfg

@@ -4,11 +4,12 @@ extends =
 
 [virtual-env-base]
 recipe = slapos.recipe.build
-_name = ${:_buildout_section_name_}
+name = ${:_buildout_section_name_}
+default-instance = true
 init =
   from zc.buildout.easy_install import working_set
   import os
-  name = options['_name']
+  name = options['name']
   eggs = options['eggs']
   try:
     scripts = "scripts = " + options['scripts']
@@ -25,6 +26,25 @@ init =
   <= python-interpreter
   eggs += %(eggs)s
   """ % locals())
+
+  if is_true(options.get('default-instance')):
+    self.buildout.parse("""
+    [.%(name)s.instance]
+    recipe = slapos.recipe.template
+    output = ${buildout:directory}/instance.cfg
+    depends = ${slapos-cookbook:recipe}
+    inline =
+      [buildout]
+      parts = publish
+
+      eggs-directory = ${buildout:eggs-directory}
+      develop-eggs-directory = ${buildout:develop-eggs-directory}
+
+      [publish]
+      recipe = slapos.cookbook:publish
+      activate-script = %(location)s
+    """ % locals())
+
 install =
   with open(location, "w") as f:
     f.write(options['template'] % {