check if oauth headers are available before creating request token

[Steve Martinelli]

Before continuing to create a request token, and making assumptions that all the headers are there; and giving a poor error message when they are not. We should have a better check, and one that advises the user to change their Apache config, since that is likely the problem.

[Steve Martinelli (stevemar)]

patch is here: https://review.openstack.org/#/c/142191/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/142191
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=4f7d17b4bd94cc4c2e9beef49eb823aab8c3a234
Submitter: Jenkins
Branch: master

commit 4f7d17b4bd94cc4c2e9beef49eb823aab8c3a234
Author: Steve Martinelli <email address hidden>
Date: Tue Dec 16 14:06:58 2014 -0500

    Provide additional detail if OAuth headers are missing

    If WSGIPassAuthorization is not set correctly, the user gets back
    an obscure message, since the code continues and tries to get
    values from a None object.

    This change brings a proper exception for this configuration issue
    and lets the user know what to fix.

    Closes-Bug: #1420121

    Change-Id: Iee282383a67ec13b5bfb5267fe9d81124c5e289d