ipa-replica-prepare: Wait for the DNS entry to be resolvable

It takes some time after the DNS record is added until it propagates
to Bind. In automated installations, it might happen that
replica-install is attempted before the hostname is resolvable;
in that case the connection check would fail.

Wait for the name to be resolvable at the end of replica-prepare.
Mention that this can be interrupted (Ctrl+C).
Provide an option to skip the wait.

In case DNS is not managed by IPA, this reminds the admin of the necessary
configuration and checks their work, but it's possible to skip (either by
interrupting it interactively, or by the option).
dirty hack for test diagnosis