slaprunner: keep old recipe eggs otherwise instance can't be upgraded

As we have runners with a section deployed using
collective.recipe.shelloutput, if collective.recipe.shelloutput isn't in
the SR folder anymore thisi section can't be uninstalled (as the
uninstall method is defined in the egg).

The output of buildout for this error was :

While:
  Installing.
  Uninstalling runner-sshkeys-publickey-fingerprint-shelloutput.
  Installing recipe collective.recipe.shelloutput.
  Getting distribution for 'collective.recipe.shelloutput'.
Error: We don't have a distribution for collective.recipe.shelloutput
and can't install one in offline (no-install) mode.
While:
  Installing switch_softwaretype.

The cause was f936ea2c

software/slaprunner/software.cfg

@@ -151,6 +151,9 @@ eggs +=
 # for gunicorn[gthread]
   futures
   supervisor
+# BBB: eggs used as recipe should be kept otherwise sections depending
+# on it can't be uninstalled
+  collective.recipe.shelloutput
 
 [versions]
 Flask-Auth = 0.85

[Julien Muchembled]

Since collective.recipe.shelloutput does not have a zc.buildout.uninstall entry point, that's stupid. We should fix buildout to remember which egg needs to be there for uninstall.

Another thing is that we want to remove all usage of collective.recipe.shelloutput. Now that it's available again, people of less discouraged from using it. That's not the first time I want to prevent usage of broken recipes or even full eggs. Another buildout feature we should implement.

/cc @jerome @kazuhiko

[Jérome Perrin]

Since collective.recipe.shelloutput does not have a zc.buildout.uninstall entry point, that's stupid. We should fix buildout to remember which egg needs to be there for uninstall.

Ah that's nice idea.