Provide a configuration option to force a zone signing through after N failed tries.

Add an option where a user can specify a parameter
to control how many failed signing attempts (or how long) the signer waits
until it resorts to forcing the signing through with the equivalent of:

ods-signer clear <zone>
ods-signer sign <zone>

Without this parameter defined then, by default, the system would still continue to back off.