Remove project id in ViewBuilder alternate link

Clearly nobody really uses the "application/vnd.openstack.image"
links in the returned results from GET /v2/{tenant}/images
REST API call, since the link URI returned in it is wrong.

Glance URIs do *not* contain a project or tenant in the URI
structure like Nova's REST API URIs do, but _get_alternate_link()
method of the image ViewBuilder tacks it on improperly:

Change-Id: I4ccb5628569c60026a1772df0794ac0271c48db3
Closes-Bug: #1343080
Add API schema for v2.1 "resize a server" API

Some v2.1 APIs(create/update/rebuild server) contains the API
extension feature, it searches extension methods with its method
name and operates them automatically.

It is necessary to change the API schemas also automatically based
on the API extension loading condition, because the API extensions
add API parameters.

This patch adds API schema extensions which are implemented with
the same mechanism (stevedore library) as the API extension for "resize
a server" extensions.

Partially implements blueprint v2-on-v3-api

Change-Id: I3651da8c1d23ee1b5d4710b1b323ecf9337ca70d
Merge "Remove project id in ViewBuilder alternate link"
Merge "Add API schema for v2.1 "resize a server" API"