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