obs/re6st: fix import of slapos.libnetworkcache

The commit c5e509c3
added the ability to download from network cache when building re6st,
but slapos.libnetworkcache is imported after bin/buildout has
already been generated. The fixup consists of adding libnetworkcache
in bin/buildout from bin/python, which has been renamed to
bin/python.temp until the end of bootstrap to start again if we fail
before the end of the task.

obs/re6st/buildout.cfg.in

@@ -17,7 +17,7 @@ parts += chrpath python
 
 [python]
 recipe = zc.recipe.egg
-interpreter = ${:_buildout_section_name_}
+interpreter = ${:_buildout_section_name_}.tmp
 eggs = slapos.libnetworkcache
 # https://lab.nexedi.com/nexedi/slapos.buildout/merge_requests/11
 scripts = dummy

obs/re6st/make.py

@@ -97,6 +97,8 @@ def bootstrap(task):
                 "--setuptools-version", "33.1.0"), input=bootstrap)
             check_call(("bin/buildout", "buildout:extensions=",
                 "buildout:newest=true", "buildout:parts=python"))
+            check_call(("bin/python.tmp", "bin/buildout", "bootstrap"))
+            os.rename("bin/python.tmp", "bin/python")
 
 def sdist_version(egg):
     global MTIME, VERSION