apt install maas fails without default gateway

[hogetaro]

apt install maas ends up with error, without default gateway defined on the machine.
Ubuntu 16.04, MAAS Version 2.0.0 (rc2+bzr5156)

apt install maas output
------------------------
For full output , see attachment.
```
(snip...)
Setting up maas-region-controller (2.0.0~rc2+bzr5156-0ubuntu1~16.04.2) ...
Device "" does not exist.
dpkg: error processing package maas-region-controller (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of maas:
 maas depends on maas-region-controller (= 2.0.0~rc2+bzr5156-0ubuntu1~16.04.2); however:
  Package maas-region-controller is not configured yet.

dpkg: error processing package maas (--configure):
 dependency problems - leaving unconfigured
Processing triggers for ureadahead (0.100.0-19) ...
No apport report written because the error message indicates its a followup error from a previous failure.
Processing triggers for systemd (229-4ubuntu4) ...
Processing triggers for libc-bin (2.23-0ubuntu3) ...
Errors were encountered while processing:
 maas-region-controller
 maas
E: Sub-process /usr/bin/dpkg returned an error code (1)
```

Steps to reproduce.
--------------------
1. Prepare VBoxMachine with configuration...
1.2 Create 2 HostOnlyNetworks (10.0.0.1/24 , 10.1.0.1/24 as Host's NIC ), without DHCP
1.3 Create GuestVM with, 2GB Mem, 40Gb Disk, 2 NICs (both connected to each HostOnlyNetwork)
2. Install Ubuntu 16.04 on the GuestVM
2.1 Set both NIC with static address *without gateway* (really no gw there)
2.2 Set http proxy 10.1.0.1:3128
3. just install as 'sudo apt install maas'

Network topology
-------------------

    Upstream http-proxy (Not an ip-reachable route, just http gateway )
      |
-------------
  |
 VBoxHost
  | Host's NIC 10.1.0.1 (Provides http-proxy. Don't work as network gateway)
------------ HostOnlyNetwork1 (10.1.0.0/24)
  |
 Guest(MAAS)
  |
~~~~~~~~~~~ HostOnlyNetwork2 (10.0.0.0/24)
| |
Node1 Node2 ... (to be controlled under MAAS)

Bugs
--------------
1. Installation process completely hangs.
   (because of /var/lib/dpkg/info/maas-region-controller.postinst#get_default_route_ip() failure)
2. Error message does not tell user any suggestion.
3. Using default gateway as maas/default-maas-url seems not a good strategy.
   In many evaluating case ,region-controller and rack-controller should resides
   on same machine.
   why don't you use ip address of first(or second) NIC ?