Fix zope instance home when the instance is not given.

stack/erp5/buildout.cfg

@@ -306,7 +306,7 @@ md5sum = d1cf938074b4b2f407122a40991bfef2
 [template-zope]
 < = download-base
 filename = instance-zope.cfg.in
-md5sum = 6d069b2e3236db7af542822b4822c492
+md5sum = c172319dcfa932f82181e3affe807fc4
 link-binary =
   ${aspell:location}/bin/aspell
   ${dmtx-utils:location}/bin/dmtxwrite

stack/erp5/instance-zope.cfg.in

@@ -46,7 +46,7 @@ ca-crl = ${directory:test-ca-crl}
 recipe = slapos.cookbook:mkdirectory
 bin = ${buildout:directory}/bin
 etc = ${buildout:directory}/etc
-instance =  {{slapparameter_dict.get('instance', '${:srv}/erp5shared')}}
+instance =  {{slapparameter_dict.get('instance') or ${:srv}/erp5shared}}
 instance-constraint = ${:instance}/Constraint
 instance-document = ${:instance}/Document
 instance-etc = ${:instance}/etc