test: dbus: passive read interface

Added basic unit-tests and added a factory for creating the
DbusPassive read interface so that it can be nicely error checked.  This
is handled via a valid type check where the only valid types are 'fan'
and 'temp'.

Change-Id: I558ed09bf509d26f20c6e431bb0789074e9aa841
Signed-off-by: Patrick Venture <venture@google.com>
7 files changed