Export 'On Hold' email addresses as 'opted out'

CiviCRM's bounce processing marks addresses with hard bounces as
'On Hold'.  We shouldn't send emails to these addresses in Silverpop,
so this commit exports 'On Hold' email addresses the same as opted
out or 'do not email' contact records.

Change-Id: I4b36dd63b62d1723356313c24d7ba33dd47ef8b1