Fix a few cosmetic issues with `rndc managed-keys`

Fix a few cosmetic issues with `rndc managed-keys`

The handling of class and view arguments was broken, because the code
didn't realise that next_token() would overwrite the class name when
it parsed the view name. The code was trying to implement a syntax
like `refresh [[class] view]`, but it was documented to have a syntax
like `refresh [class [view]]`. The latter is consistent with other rndc
commands, so that is how I have fixed it.

Before:

$ rndc managed-keys refresh in rec
rndc: 'managed-keys' failed: unknown class/type
unknown class 'rec'

After:

$ rndc managed-keys refresh in rec
refreshing managed keys for 'rec'

There were missing newlines in the output from `rndc managed-keys
refresh` and `rndc managed-keys destroy`.

Before:

$ rndc managed-keys refresh
refreshing managed keys for 'rec'refreshing managed keys for 'auth'

After:

$ rndc managed-keys refresh
refreshing managed keys for 'rec'
refreshing managed keys for 'auth'

(cherry picked from commit 6a3b851f72929802fc10a51f17b170db54988021)