add permission alter to idomysql docs

[lbetz]

got this one:
Notice: /Stage[main]/Icinga2::Feature::Idomysql/Exec[idomysql_import_schema]/returns: ERROR 1142 (42000) at line 1436: ALTER command denied to user 'icinga2'@'localhost' for table 'icinga_servicestatus'
Error: mysql -h '127.0.0.1' -u 'icinga2' -p'icinga2' 'icinga2' < '/usr/share/icinga2-ido-mysql/schema/mysql.sql' returned 1 instead of one of [0]
Error: /Stage[main]/Icinga2::Feature::Idomysql/Exec[idomysql_import_schema]/returns: change from notrun to 0 failed: mysql -h '127.0.0.1' -u 'icinga2' -p'icinga2' 'icinga2' < '/usr/share/icinga2-ido-mysql/schema/mysql.sql' returned 1 instead of one of [0]

means alter is missing into grant
grant => ['SELECT', 'INSERT', 'UPDATE', 'DELETE', 'DROP', 'CREATE VIEW', 'CREATE', 'INDEX', 'EXECUTE'],