splitting ssl cert generation script from ca cert generation script and ...

...updating docs accordingly

Jeff brought up a good point today that we should split the scripts for CA cert and SSL cert generation. This way, if users need to update their SSL certs keeping the old CA certs, they can do that. This will especially be useful going forward, so that the manual step of copying over CA cert and adding it to system trusted cert for consumers as well as pulp-admin hosts doesn't need to be performed again and again.