Add messaging hostname validation

[nasark]

When configuring messaging on an appliance, we should check to see that the hostname is reachable and valid before proceeding with the current configuration. Currently we allow users to enter any hostname and in the event of an incorrect hostname that is entered, the messaging will only fail after the appliance configuration. This can cause unnecessary confusion for users and can be avoided

@miq-bot assign @nasark
@miq-bot add_label enhancement

[miq-bot]

@nasark 'nasark' is an invalid assignee, ignoring...

[miq-bot]

This issue has been automatically marked as stale because it has not been updated for at least 3 months.

If you can still reproduce this issue on the current release or on master, please reply with all of the information you have about it in order to keep the issue open.