Improve the sample keystone.conf
Improve the sample keystone.conf

Make sure all the available options are include in the file, add
some more documentation and, rather than set any of the defaults,
just include them as comments.

Change-Id: I2cb6060f47ea88349b1862d4d995c80cf9237066

ilay09/keystone,jamielennox/keystone,savi-dev/keystone,rodrigods/keystone,jumpstarter-io/keystone,vivekdhayaal/keystone,savi-dev/keystone,derekchiang/keystone,ilay09/keystone,blueboxgroup/keystone,ging/keystone,roopali8/keystone,nuxeh/keystone,townbull/keystone-dtrust,kwss/keystone,citrix-openstack-build/keystone,blueboxgroup/keystone,himanshu-setia/keystone,mahak/keystone,jonnary/keystone,dsiddharth/access-keys,jonnary/keystone,takeshineshiro/keystone,citrix-openstack-build/keystone,dstanek/keystone,ajayaa/keystone,maestro-hybrid-cloud/keystone,cbrucks/Federated_Keystone,cbrucks/Federated_Keystone,rushiagr/keystone,promptworks/keystone,ntt-sic/keystone,JioCloud/keystone,cernops/keystone,cloudbau/keystone,takeshineshiro/keystone,promptworks/keystone,roopali8/keystone,mahak/keystone,nuxeh/keystone,JioCloud/keystone,jamielennox/keystone,dstanek/keystone,rickerc/keystone_audit,UTSA-ICS/keystone-kerberos,openstack/keystone,cernops/keystone,vivekdhayaal/keystone,savi-dev/keystone,cloudbau/keystone,rajalokan/keystone,dstanek/keystone,reeshupatel/demo,idjaw/keystone,rodrigods/keystone,townbull/keystone-dtrust,klmitch/keystone,MaheshIBM/keystone,derekchiang/keystone,himanshu-setia/keystone,rushiagr/keystone,rickerc/keystone_audit,nuxeh/keystone,jumpstarter-io/keystone,cbrucks/Federated_Keystone,citrix-openstack-build/keystone,kwss/keystone,mahak/keystone,vivekdhayaal/keystone,rajalokan/keystone,ilay09/keystone,reeshupatel/demo,klmitch/keystone,jumpstarter-io/keystone,cloudbau/keystone,dims/keystone,openstack/keystone,kwss/keystone,ging/keystone,MaheshIBM/keystone,openstack/keystone,UTSA-ICS/keystone-kerberos,reeshupatel/demo,ntt-sic/keystone,dims/keystone,townbull/keystone-dtrust,maestro-hybrid-cloud/keystone,rajalokan/keystone,rickerc/keystone_audit,dsiddharth/access-keys,ntt-sic/keystone,ajayaa/keystone,dsiddharth/access-keys,derekchiang/keystone,rushiagr/keystone,promptworks/keystone,idjaw/keystone