Cluster scaling: deletion

Inmplemented:
* exclude/include files mechanism is implemented
* adding instances was change
* removing instances works ok
* "slaves" and "masters" are deleted

Implements blueprint delete-instances
Implements blueprint get-rid-of-slaves-file
Fixes: bug #1199884

Change-Id: Ie1bfaa421fce22efd3115ba13758932b6b592d7a