Add algorithmic option for restricted allocation
Add algorithmic option for restricted allocation

Restricting allocation to a specified set of nodes is
needed for allocation in the presence of opportunistic
locking.

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

mbakke/ganeti,leshchevds/ganeti,andir/ganeti,bitemyapp/ganeti,ganeti/ganeti,ganeti/ganeti,grnet/snf-ganeti,leshchevds/ganeti,andir/ganeti,bitemyapp/ganeti,yiannist/ganeti,yiannist/ganeti,grnet/snf-ganeti,mbakke/ganeti,onponomarev/ganeti,mbakke/ganeti,yiannist/ganeti,andir/ganeti,ganeti/ganeti,leshchevds/ganeti,onponomarev/ganeti