Make db creation more graceful.

The DB is replicated in install scenarios, so make sure to not create
it twice.

db_scripts/diff/13840_not_replicated.up

@@ -1,6 +1,6 @@
 -- don't replicate this up script to not break 2.8->3.0 upgrade
 
-CREATE DATABASE prosody;
+CREATE DATABASE IF NOT EXISTS prosody;
 GRANT ALL PRIVILEGES ON prosody.* TO 'prosody'@'localhost' IDENTIFIED BY 'PW_PROSODY';
 GRANT SELECT ON provisioning.voip_preferences TO prosody@localhost;
 GRANT SELECT ON provisioning.voip_usr_preferences TO prosody@localhost;