move usage_audit to cmd/eventlet package

setup_rpc func need the eventlet monkey_patch,
    otherwise the main process will be blocked.

Change-Id: I9f4a0b7c957b7dc7740e3cf6e75f18778ad562d0
Closes-Bug: #1522681
(cherry picked from commit 5b6992db49)

setup.cfg

@@ -97,7 +97,7 @@ console_scripts =
     neutron-rpc-server = neutron.cmd.eventlet.server:main_rpc_eventlet
     neutron-rootwrap = oslo_rootwrap.cmd:main
     neutron-rootwrap-daemon = oslo_rootwrap.cmd:daemon
-    neutron-usage-audit = neutron.cmd.usage_audit:main
+    neutron-usage-audit = neutron.cmd.eventlet.usage_audit:main
     neutron-metering-agent = neutron.cmd.eventlet.services.metering_agent:main
     neutron-sriov-nic-agent = neutron.plugins.ml2.drivers.mech_sriov.agent.sriov_nic_agent:main
     neutron-sanity-check = neutron.cmd.sanity_check:main