Change occurrences of keystone to identity server

The auth token middleware referred to Keystone everywhere, but
Keystone is only one possible implementation of the identity API.
The code should refer to the identity API or identity server where
appropriate.

Change-Id: I67a0c203a4e0482b36b021e98e8ac99e29b0c2df
Correct tests to use strings in conf

When paste passes the conf to the auth_token middleware all of the
values are strings. The tests should also pass all the conf values
as strings.

Change-Id: I2001b74b5a3e6f762f7f298c217856dc56eb81fa
Merge "Change occurrences of keystone to identity server"
Merge "Correct tests to use strings in conf"