* Defaults for apiserver_loadbalancer_domain_name

When loadbalancer_apiserver is defined, use the
apiserver_loadbalancer_domain_name with a given default value.

Fix unconsistencies for checking if apiserver_loadbalancer_domain_name
is defined AND using it with a default value provided at once.

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

* Define defaults for LB modes in common defaults

Adjust the defaults for apiserver_loadbalancer_domain_name and
loadbalancer_apiserver_localhost to come from a single source, which is
kubespray-defaults. Removes some confusion and simplefies the code.

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>