Create macros.cfg file to generate a virtual environment

See merge request nexedi/slapos!1135

component/macros/virtual-env.cfg

+[buildout]
+extends =
+	../pygolang/buildout.cfg
+
+[virtual-env-base]
+recipe = slapos.recipe.build
+_name = ${:_buildout_section_name_}
+init =
+  from zc.buildout.easy_install import working_set
+  import os
+  name = options['_name']
+  eggs = options['eggs']
+  try:
+    scripts = "scripts = " + options['scripts']
+  except KeyError:
+    scripts = ""
+
+  self.buildout.parse("""
+  [.%(name)s.install-eggs]
+  recipe = zc.recipe.egg
+  eggs = %(eggs)s
+  %(scripts)s
+
+  [.%(name)s.install-interpreter]
+  <= python-interpreter
+  eggs += %(eggs)s
+  """ % locals())
+install =
+  with open(location, "w") as f:
+    f.write(options['template'] % {
+      "path" : self.buildout['buildout']['bin-directory'],
+      "name" : self.name,
+    })
+
+# Template virtual env for bash shell in posix
+[virtual-env-base:posix]
+template =
+  deactivate () {
+    set PATH PS1
+    while [ "$1" ]; do
+      eval "if [ \"\$_OLD_VENV_$1\" ]; then $1=\$_OLD_VENV_$1; else unset $1; fi; unset \$_OLD_VENV_$1"
+      shift
+    done
+    unset -f deactivate
+  }
+
+
+  VENV_PATH=%(path)s
+  _OLD_VENV_PATH=$PATH
+  _OLD_VENV_PS1=$PS1
+  PATH=$VENV_PATH:$PATH
+  PS1='(%(name)s) '$PS1

software/django-dev/software.cfg

+[buildout]
+extends =
+  ../../stack/slapos.cfg
+  ../../component/macros/virtual-env.cfg
+
+parts =
+  instance
+  slapos-cookbook
+
+[python]
+part = python3
+
+[django-env]
+<= virtual-env-base
+location = ${buildout:directory}/activate
+eggs = Django
+
+[instance]
+recipe = slapos.recipe.template
+output = ${buildout:directory}/instance.cfg
+inline =
+  [buildout]
+  parts = publish
+
+  eggs-directory = ${buildout:eggs-directory}
+  develop-eggs-directory = ${buildout:develop-eggs-directory}
+
+  [publish]
+  recipe = slapos.cookbook:publish
+  activate-script = ${django-env:location}
+
+[versions]
+Django = 3.2.12
+sqlparse = 0.4.2
+pytz = 2021.3
+asgiref = 3.3.2
+typing-extensions = 4.1.1:whl