missing signing.ca_key in sample configuration

[Jianing Yang]

People who run `keystone-manage pki_setup' in normal user may get an exception 'OSError: [Errno 13] Permission denied: '/etc/keystone' (which is an unclear message) since they don't know that signing.ca_key has also to be set to a writable file by reading sample configuration.

I suggest show the default value of signing.ca_key in the sample configuration to give people a clue.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/32260

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/32260
Committed: http://github.com/openstack/keystone/commit/cef5dec5bf4a6446946d2271d5c99b5d5160ae1a
Submitter: Jenkins
Branch: master

commit cef5dec5bf4a6446946d2271d5c99b5d5160ae1a
Author: Jianing YANG <email address hidden>
Date: Sun Jun 9 10:48:32 2013 +0800

    add ca_key to sample configuration

    this gives end-users a clue that they also have to set
    ca_key for using ssl certificates other than the default
    place /etc/ssl.

    Change-Id: I41c4118d02723730c0ba183add866a0e0fa67e7b
    Fixes: Bug #1188956