checkconf: check key existence in views

checkconf: check key existence in views

Commit `2956e4fc45b3c2142a3351682d4200647448f193` hardened the `key`
name check when used in `primaries` to reject the configuration if
the key was not defined, rather than simply checking whether the
key name was correctly formed.

However, the key name check didn't include the view configuration,
causing keys not to be recognized if they were defined inside the
view and not at the global level.  This regression is now fixed.