All of the inspector interface methods takes in instance being
inspected and duration of seconds over which metric needs to be
calculated. Though the duration parameter is not used, the
method signaures need to be updated to match ceilometer
changes [1].
[1] 90560e42fd1b589ebb03b8629cf591dee8e559a6
Change-Id: I3ad8da0dc9cd26e269bf18f26231063d122faf98
e8c77a02e0