ipalib: host_del: Extend LDAPDelete's takes_options instead of overriding

The host-del command did not accept --continue option, since the
takes_options was overriden and did not take the options from LDAPDelete.

Fix the behaviour.

https://fedorahosted.org/freeipa/ticket/4473

Reviewed-By: Jan Cholasta <jcholast@redhat.com>