NC migration (checkpoint).

- Verify incoming instance lists for migrations.

Implements EUCA-5178.
Merge branch 'dev/juphoff/evac' of git.eucalyptus-systems.com:eucalyptus into dev/juphoff/evac
[NC] Loop over entire list of instances to migrate (rather than using only first entry).

Implements EUCA-5178.
[CC] handle migration-by-instanceId request with "not yet supported" log message.
Merge branch 'dev/juphoff/evac' of git.eucalyptus-systems.com:eucalyptus into dev/juphoff/evac
Merge remote-tracking branch 'origin/dev/juphoff/evac' into team/evac

Conflicts:
	cluster/handlers.c
Fix old copypaste bugs in migrateinstances.py
Add a --stop-node option to euca-migrate-instances

Fixes EUCA-5094
[CC] Assemble and send multiple-instance migration requests to nodes.

Implements EUCA-5175.
NC migration development.

- Use entire list of to-migrate instances in requests.
- Improve handling of duplicate migration requests.

Implements EUCA-5178.
[NC] Tweaks to enable concurrent-instance migrations.

Implements EUCA-5178.
CC migration development.

- Partially implemented migrations specified by instance ID.
- Implemented concurrent-instance migrations.

Implements EUCA-5175, EUCA-5069.
Merge branch 'testing' into team/evac
Merge remote-tracking branch 'origin/dev/dmitrii/testing' into dev/juphoff/evac

Conflicts:
	cluster/handlers.c
CC migration development.

- Trim & neaten debug logging.
- Set local instance-cache migration state to 'preparing' for instances
  after 'prepare' call to source node returns.

Implements EUCA-5069, EUCA-5175.
[CC] Only schedule migrations to nodes that are ENABLED.

Implements EUCA-5175.
Rename --stop-node -> --stop-source
Merge remote-tracking branch 'origin/dev/juphoff/evac' into team/evac

Conflicts:
	cluster/handlers.c
Merge remote-tracking branch 'origin/dev/juphoff/evac' into team/evac
Merge remote-tracking branch 'origin/testing' into team/evac