3G: Unable to connect to gsm modem using fake-gsm-modem

Shill crashed when it tried to interact with fake-gsm-modem, because
flimflam_test.py did not respond to some DBus messages. This CL
implements the following DBus properties:

    org.freedesktop.ModemManager.Modem.Gsm.Network:

        AllowedMode
        AccessTechnology

    org.freedesktop.ModemManager.Modem.Gsm.Card:

        EnabledFacilityLocks

    org.freedesktop.ModemManager.Modem and
    org.freedesktop.ModemManager.Modem.Cdma:

        Changed MEID to Meid

This CL also updates the steps to test shill using fake-gsm-modem as
described in the comments in fake-gsm-modem.

BUG=chromium-os:34552
TEST=Repeated the following steps on a Lumpy with GOBI3000 modem:

    $ stop flimflam
    $ stop cromo
    $ /usr/local/lib/flimflam/test/veth setup pseudomodem0 172.16.1
    $ /usr/local/lib/flimflam/test/fake-gsm-modem -c tmobile --shill
    $ start flimflam

    T-Mobile should appear as a connectable network in the UI.
    Furthermore, running 'modem status' in crosh should display
    info for TestModem. shill shouldn't crash.

    Cleanup:
    $ stop flimflam
    $ # kill fake-gsm-modem
    $ /usr/local/lib/flimflam/test/veth teardown pseudomodem0
    $ start cromo
    $ start flimflam

Change-Id: If1060e2816e6a720ee258adbbc7b2a6c230915c1
Reviewed-on: https://gerrit.chromium.org/gerrit/34154
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Arman Uguray <armansito@chromium.org>
Tested-by: Arman Uguray <armansito@chromium.org>
2 files changed