Fix private parameters wrapping when deserializing JSON
Fix private parameters wrapping when deserializing JSON

On the Python side it was assumed that the blacklisted private
parameters were always dictionaries, but since they're optional, they
could be 'None' as well.

Signed-off-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

leshchevds/ganeti,leshchevds/ganeti,yiannist/ganeti,onponomarev/ganeti,dimara/ganeti,yiannist/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,bitemyapp/ganeti,ganeti/ganeti,mbakke/ganeti,yiannist/ganeti,ganeti/ganeti,onponomarev/ganeti,mbakke/ganeti,apyrgio/ganeti,apyrgio/ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,andir/ganeti,dimara/ganeti,mbakke/ganeti,ganeti/ganeti,andir/ganeti,andir/ganeti