test: add get-network-time script

Add get-network-time script to which uses
the new NetworkTime DBus interface.  This
commit is based off of commit

2e77d435587162a2e67ab0c236f95c6680947c55

from the nemomobile tree:

https://github.com/nemomobile-packages/ofono

Author: Petri M. Gerdt <petri.gerdt@jollamobile.com>
Date:   Tue Dec 18 13:17:19 2012 +0200

nettime: Network time plugin

Some ideas and code has been adapted from a rejected
network time plugin patch by Antti Paila:
http://lists.ofono.org/pipermail/ofono/2011-January/007437.html