Allow overriding the number of test databases.

Based on work by Romain Courteaud <romain@nexedi.com>.

stack/erp5/buildout.cfg

@@ -186,7 +186,7 @@ context =
 [template-mariadb]
 < = template-jinja2-base
 filename = instance-mariadb.cfg
-md5sum = 0e8e9bfc8c8a5f1bd71f5c4f346ef68b
+md5sum = 867bd8e3c4f56db2aab2fcad59f2efd8
 extra-context =
     key coreutils_location coreutils:location
     key dcron_location dcron:location

stack/erp5/instance-mariadb.cfg.in

@@ -30,7 +30,7 @@ recipe = slapos.cookbook:generic.mysql
 
 # Options
 user = user
-parallel-test-database-amount = 100
+parallel-test-database-amount = ${slap-parameter:test-database-amount}
 port = 45678
 ip = ${slap-network-information:local-ipv4}
 database = erp5
@@ -178,3 +178,6 @@ recipe = slapos.cookbook:check_port_listening
 path = ${basedirectory:promise}/mariadb
 hostname = ${mariadb-instance:ip}
 port = ${mariadb-instance:port}
+
+[slap-parameter]
+test-database-amount = 100