Fix argument order in ReserveLV and ReserveMAC

ConfigWriter.ReserveLV() and Configwriter.ReserveMAC() called
TemporaryReservationManager.Reserve() with the ec_id and resource arguments
swapped. As a result, two reservation attempts for the same resource type
within the same LU would fail, even if the resources requested were different,
e.g.:

  $ gnt-instance add -t sharedfile -o debootstrap+default \
       --net 0:mac=00:01:02:03:04:00 \
       --net 1:mac=00:01:02:03:04:ff \
       --disk 0:size=2g  test_instance
  Failure: prerequisites not met for this operation:
  error type: resource_not_unique, error details:
  MAC address 00:01:02:03:04:ff already in use in cluster

This patch fixes the argument order in the call to Reserve().

Signed-off-by: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>