Use a utf8mb4 collation

Change I25bd7b5d2a904dad3e13efaf2da94cce205bcc0b switched the
characterset for new databases to utf8mb4, but the Puppet MySQL
module independently defaults the collate parameter to
utf_general_ci which is not compatible with utf8mb4. Set an explicit
utf8mb4_general_ci collation instead so that the database can be
created successfully.

Change-Id: I9cc715e0b0cec9494489d56a2f4c1549782b0fca

manifests/mysql.pp

@@ -33,5 +33,6 @@ class storyboard::mysql (
     host     => 'localhost',
     grant    => ['all'],
     charset  => 'utf8mb4',
+    collate  => 'utf8mb4_general_ci',
   }
 }