This framework was merged a year ago and AFAICT hasn't seen use beyond
the two initial wikimedia extensions for Nova.

The framework basically allows a way for a single plugin to register API
extensions and notification hooks. Both of these can be done by directly
using config opts like osapi_compute_extension and notification_driver
so this framework really only helps if we expected to (and wanted to)
lots of these plugins in the wild.

Nova is the only project using this and we don't have an active
maintainer listed in the MAINTAINERS file, so it seems like it's time to
remove it from the incubator.

Change-Id: I5552b5625e26f4821464807743545ec6f5117f2b

H402  one line docstring needs punctuation

Change-Id: Ie848453cace318d8310cdf0234c512f4c1121119

One code change, rest are in headers

Change-Id: I73f59681358629e1ad74e49d3d3ca13fcb5c2eb1

also,this patch turns off pep8 E125 check.

Change-Id: I22d2a94d89530586d614af39af17ae542c5e0cbf

For blueprint novaplugins.

It turns out that most of the plugin framework applies equally well
to other projects, so it's going into Nova via common so that
other projects can pull it in with a minimum of fuss.

Change-Id: Ia4455a8ca0b8c1c3e4b0b9647e8cacaf0a47c914