Clean up setting of control_exchange default

The RPC code from Oslo now registers the control_exchange option but
provides us with an API for changing the default.

blueprint: scope-config-opts
Change-Id: Ie7950daaddb53f38eb72d2a113e1f26252dd6903
update version urls to working v2 urls

the GET /v2/ API call is documented to return urls to both
wadl and pdf documents. However our call returned non working
urls to 1.1 versions of those documents. Fix this.

Also fix the unit tests to actually test the output of versions.
Previously we were over stubbing the test_verions.py so it was
testing only itself, and not the output you'd actually get from
the real versions.py module.

Renamed the variables used for the expected variables to reduce
confusion about what is an expected variable vs. the variables
coming from versions.py to try to ensure we don't have cicular
always passing tests in the future.

Fixes bug #1076109

Change-Id: I1047b8c48ff053eed5ad4afa8eae5833f70d0893
Merge "update version urls to working v2 urls"
Merge "Clean up setting of control_exchange default"