Improve the help text for the cert options
Improve the help text for the cert options

The previous commit moved all the cert options to a central location.
This commit adds additional help text to those options.

Blueprint centralize-config-options

Change-Id: Ic4d15eebefced8478e36997294264eb1951fd464

phenoxim/nova,rajalokan/nova,NeCTAR-RC/nova,klmitch/nova,vmturbo/nova,rajalokan/nova,cloudbase/nova,hanlind/nova,hanlind/nova,CEG-FYP-OpenStack/scheduler,jianghuaw/nova,BeyondTheClouds/nova,gooddata/openstack-nova,CEG-FYP-OpenStack/scheduler,Juniper/nova,rahulunair/nova,jianghuaw/nova,bigswitch/nova,alaski/nova,sebrandon1/nova,rahulunair/nova,vmturbo/nova,mikalstill/nova,BeyondTheClouds/nova,Juniper/nova,mikalstill/nova,cernops/nova,cloudbase/nova,mahak/nova,openstack/nova,cyx1231st/nova,gooddata/openstack-nova,Juniper/nova,openstack/nova,NeCTAR-RC/nova,cloudbase/nova,phenoxim/nova,rajalokan/nova,cernops/nova,dims/nova,zhimin711/nova,jianghuaw/nova,rahulunair/nova,vmturbo/nova,gooddata/openstack-nova,bigswitch/nova,gooddata/openstack-nova,cernops/nova,Juniper/nova,klmitch/nova,klmitch/nova,cyx1231st/nova,rajalokan/nova,openstack/nova,hanlind/nova,zhimin711/nova,mahak/nova,dims/nova,alaski/nova,klmitch/nova,mahak/nova,sebrandon1/nova,sebrandon1/nova,mikalstill/nova,BeyondTheClouds/nova,jianghuaw/nova,vmturbo/nova