Add a utility function to force Failover
Add a utility function to force Failover

In some cases we do not want to migrate an instance off a node.
Add a function to change all OpMigrate to a corresponding OpFailover.
This will simplify the handling of such code.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>

bitemyapp/ganeti,ganeti/ganeti,leshchevds/ganeti,andir/ganeti,mbakke/ganeti,onponomarev/ganeti,mbakke/ganeti,andir/ganeti,ganeti/ganeti,mbakke/ganeti,leshchevds/ganeti,leshchevds/ganeti,andir/ganeti,onponomarev/ganeti,bitemyapp/ganeti,ganeti/ganeti