Exclude tables/keyspaces from triggered repairs

[itskarlsson]

Schedules have a way to define what tables should not repair. It would be useful to have this possibility in triggered repairs.

There are some use cases where you wish to repair everything except for a few tables. Currently the only way this can be done is by defining every table/keyspace combination.

With #299 and #158 you could run a full repair on many tables. An option to exclude some would be good. I doubt it would be challenging to implement but I suspect that it will be difficult to do this in a neat way.