Enable Guru Meditation Reports for other refarch agents

Enable Guru Meditation Reports for other refarch agents

OVS agent already supports GMR, but LinuxBridge and SR-IOV agents don't.
To enable them for those agents, we should move their main() entry
points under neutron/cmd/, so that __init__.py code that initializes
them is triggered on their invocation.

Since we put their entrypoints under neutron/cmd/eventlet/, there is now
also no need to explicitly monkey patch stdlib for eventlet in the
agents code (neutron/cmd/eventlet/__init__.py already does it for us).
With that, there is no more code in the tree that directly patches
stdlib except neutron/cmd/eventlet/__init__.py.

Also removed a way to execute agent modules as scripts since it's not a
supported way to invoke them (instead, stevedore generated console
scripts should always be used).

Change-Id: I9b823d07a41b575334e52065eed7e6be2741e79d
Implements: blueprint guru-meditation-report