MeteringPluginRpc: Fix crash in periodic_task

Restore __init__ chain which has been broken by
commit bdcc5a46d7776f50d5ae372798a913349629d2f6 .

Closes-Bug: #1396893
Change-Id: Ia1f0357b6726ac79a22ed1666eecebac33689aa1
Merge "MeteringPluginRpc: Fix crash in periodic_task"