updated install and kickstart scripts for priorities

Until yum-plugin-priorities is moved to a product channel, the following
env variables need to be set to make sure priorities are honored:
CONF_OPTIONAL_REPO=1
CONF_RHEL_OPTIONAL_REPO=<repo base>/6Server/x86_64/optional

CONF_RHEL_OPTIONAL_REPO is only needed if using the yum install method
Merge pull request #12 from detiber/priorities-1.2

updated install and kickstart scripts for priorities
Check to see if jetty.xml has a 'host' property and only add it if it doesn't exist
Merge pull request #13 from ncdc/only-add-jetty-host-once

Check to see if jetty.xml has a 'host' property and only add if needed