Set fallback method for search-replace terms

[slam-campup]

The current search-replace function relies on wp-cli to fetch the existing remote domain name. This fails when the remote is not available, the remote is new, or in a few other conditions.

Set a method to detect whether the returned search values is a URL (and only a URL) and if fails then prompt the user for a search term manually.

Affects the values for _search_url and _replace_url