Only add the host property to jetty.xml if it doesn't already exist

Previously, if you ran openshift.sh multiple times,
/etc/activemq/jetty.xml would end up with multiple copies of the host
property line, which caused ActiveMQ to fail to start up.
Don't display grep results when searching for host property in jetty.xml
Remove trailing whitespace
Merge pull request #11 from ncdc/enterprise-1.2

Only add the host property to jetty.xml if it doesn't already exist