Option to suppress drush vrd's purl_base_domain message.  #2487

The warning about the purl_base_domain uses a drush_confirm dialog, which causes our post-db-copy script to hang, waiting for input.  I added an option to suppress that message so the command can be run non-interactively.
Merge pull request #2582 from openscholar/2487-hide_purl_msg

Option to suppress drush vrd's purl_base_domain message.  #2487