engine: Fixed VM sorting according to IP

VMs are now sorted numerically rather than lexicographically, by
applying the database function fn_get_comparable_ip_list in the search
mechanism.

Change-Id: Ic555ef3c16e8cd88d53314f2b990861ef301508a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=895468
Signed-off-by: Lior Vernia <lvernia@redhat.com>