Ignore dupicate databases in mxs1849_table_sharding

The test environment isn't always pristine after a test run so for the
sake of being able to actually test what we're attempting to test, we
should ignore duplicate databases for the time being.

The long-term fix is detect when a test doesn't clean up after itself.

maxscale-system-test/cnf/maxscale.cnf.template.mxs1849_table_sharding

@@ -16,6 +16,7 @@ servers=server1,server2,server3,server4
 user=maxskysql
 password=skysql
 auth_all_servers=1
+ignore_databases_regex=.*
 
 [Sharding Listener]
 type=listener