erp5: fix kumofs instanciation

This was broken since commit 690be0d0
("Merge branch 'master' into erp5-cluster").

stack/erp5/buildout.cfg

@@ -182,7 +182,7 @@ link-binary =
 [template-kumofs]
 < = download-base
 filename = instance-kumofs.cfg.in
-md5sum = 00e29ccfdd2b482f7d0db35a85af2877
+md5sum = 7d9760fe65f454700342eeffec14c884
 
 [template-cloudooo]
 < = download-base

stack/erp5/instance-kumofs.cfg.in

@@ -72,7 +72,8 @@ recipe = slapos.cookbook:mkdirectory
 log = ${buildout:directory}/var/log
 services = ${buildout:directory}/etc/run
 promise = ${buildout:directory}/etc/promise
-kumofs-data = ${buildout:directory}/srv/kumofs
+srv = ${buildout:directory}/srv
+kumofs-data = ${:srv}/kumofs
 
 [resiliency-exclude-file]
 # Generate rdiff exclude file in case of resiliency