Add support for reboot/kill with FDB client

[johscheuer]

In the 7.0 release the FDB client has a new method fdb_database_reboot_worker that allows to reboot/kill workers, we should make use of that method instead of using directly fdbcli. Before we can use that method we have to expose it in the go client. Under the hood the same mechanism as for the fdbcli kill command is used.