UI fix to make sure for a destroyed/stopped vm we don't look up host tag for the host it may be running.
CLOUDSTACK-4572: findHostsForMigration API does not return correct host list

Changes:
Expected behavior:
The api should return the list of suitable/unsuitable hosts
Added fix that creates a deep copy of the the variable allHosts and prevents faulty host list return.
(cherry picked from commit 6354604eedff0c5f4ddef4940ce02df80adb656c)

Signed-off-by: animesh <animesh@apache.org>