CA-62302: Add an API call to declare a host dead

Also execute the post_declare_dead script on host.destroy

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
CA-62302: Add a cli command to declare a host dead

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #1126 from jonludlam/CA-62302-v3

CA-62302