add REPLICATION CLIENT privilege to user mysql roadmin

[ldangeard-orange]

For prometheus mysqld_exporter, we use roadmin@localhost user mysql (better than root@localhost). mysqld_exporter needs REPLICATION CLIENT privilege to monitor binlogs size.

Without this privilege we have error messages in mysql_exporter log, such as:

time="2017-09-28T12:19:57Z" level=error msg="Error scraping for collect.binlog_size: Error 1227: Access denied; you need (at least one of) the SUPER, REPLICATION CLIENT privilege(s) for this operation" source="mysqld_exporter.go:335"

The REPLICATION CLIENT privilege enables the use of the SHOW MASTER STATUS, SHOW SLAVE STATUS, and SHOW BINARY LOGS statements.

[gberche-orange]

thanks @ldangeard-orange for this PR. Please mention in the PR text what tests were run out of https://github.com/orange-cloudfoundry/cf-mysql-release/blob/master/CONTRIBUTING.md#submit-a-pull-request.

Looking at cloudfoundry-attic/mariadb_ctrl@5fa15a4...d746a00 it looks like there are associated tests to the ROadmin user that might need update.

[ldangeard-orange]

Issues cloudfoundry#184 is accepted.
I close sthis PR