Apply six for metaclass

__metaclass__ cannot be used in python3.
six be used in general for python 3 compatibility.

Change-Id: I1d9909d70bb614c9d1c336d0c492027f5b6b5088
Closes-Bug: #1236648
Make sample pipeline optional

This patch makes it possible to turn off the sample pipeline
and decouples the AMQP consumer configuration for the collector
from the sample plugins. This will make it easier to stand up
different types of pipelines in the future.

Change-Id: I10a0e54510b532d8e948e372078278dbf011f06c
Related-To: blueprint notification-pipelines
second revision, WIP

Change-Id: I894def28ee512cf3134214346968a3b6f2682af3
switched to using EnabledExtensionManager to black-list extensions

Change-Id: I50f65e5faa49c3f3cdc698deb513a943a048ca96
removed initialize_service_hook logic for store_events

Change-Id: I9625751f504377b6903ccbba462949a15e4ad97a
moved to using built-in map for sample extensions

Change-Id: I863fcfda8d983705133a7aab63602c129af64ddc
clean up

Change-Id: I69751b147755aee3ce736d7d98db08437a58d456
clean up 2

Change-Id: I09bc2fbee3f65a020359e5ae2f70a9cc34dc5391
clean up and a few new tests

Change-Id: I02db104e505fbc60ba2bc3d027ab38a918fc77d1
test_initialize_service_hook

Change-Id: Ib7abaad7c4cc0f9c255a2ed17c50b659682f444e