migration: Change name of live migration thread

migration: Change name of live migration thread

Change the name of live migration thread from 'migration'
to 'live_migration' to identify it clearly. 'migration'
is a generic word and kernel also has  tasks for process
migration with the name 'migration/cpu#'.

Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
Message-Id: <1485178976-15225-1-git-send-email-pagupta@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>