hooks framework raises if called with unregistered name

[Jay R. Wren]

There is really no good reason for this to be a raise.

It would be nice if it were a log message and not a raise.

This would allow an otherwise perfectly good charm to continue to function even though there is some odd, unused configuration.

https://jujucharms.com/docs/stable/authors-hook-errors says "If any of your hooks returns a non-zero exit code, juju will stop managing the unit directly and will wait for user intervention. This is a Bad Thing, and you should make every effort to avoid it, because the average user may not be in a position to diagnose the fault with any great degree of sophistication." Charm helpers should help to avoid non-zero exit code.