Create fdbcli command to force terminate all backup/DR mutation streams on a cluster

From [Aborting a DR/backup when destination is unreachable](https://forums.foundationdb.org/t/aborting-a-dr-backup-when-destination-is-unreachable/1098/), if you `fdbdr --abort` without `--cleanup`, and then destroy the secondary cluster forever, the only way to get out of that situation is to manually issue `clearrange` commands.

We should build an equivalent command into fdbcli, as we probably don't wish for any operational changes to require manual set/clearrange commands.