neutron-metering-agent package name is wrong

In Ubuntu the neutron-metering-agent is actually found in the
neutron-plugin-metering-agent package.

Change-Id: Id93ff8adfdb208a2ac56663c4f3c457c6e3d9135
Partial-Bug: #1284179
(cherry picked from commit 685dc32f153faa9443030f63e43c01a96f52711b)