Fix evacuation out of drained node

Fix evacuation out of drained node

* fix node daemon not to skip data, such as, memory and disk size,
  when building the node list to send to HBal, given that these data
  are important for HBal to determine whether an evacuation is
  possible
* fix iallocator to properly load drained nodes from the list passed
  by the node daemon, instead of zeroing all the data, such as, the
  memory and disk size
* this fixes issue 615

Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>