Do not allow networks with less than 8 hosts

This is only needed in case base64 and bitarray.tostring() is used for
saving reservations. If bitarray.to01() was used then we would not have
this restriction.

Signed-off-by: Dimitris Aragriorgs <dimara@grnet.gr>

lib/network.py

@@ -75,6 +75,7 @@ class AddressPool(object):
       self.ext_reservations = bitarray(self.network.numhosts)
       self.ext_reservations.setall(False)
 
+    assert self.network.numhosts >= 8
     assert len(self.reservations) == self.network.numhosts
     assert len(self.ext_reservations) == self.network.numhosts