Register should return absolute HTTP URL.

Currently, when registering a channel with the SimplePush server a relative endpoint url is returned. This is not spec compliant as the spec shows that the pushEndpoint should be an absolute URL.

This task should fix this and have an absolute URL returned. Keep in mind that that this must work in an environment like OpenShift.

We also need to verify that this does not have implications on the UnifiedPush Server as it currently takes a 'pushNetworkURL' as a parameter when registering the variant, as in:

curl -v -H "Accept: application/json" -H "Content-type: application/json" -X POST -d '{"pushNetworkURL" : "https://localhost:7777/endpoint/"}' http://localhost:8080/ag-push/rest/applications/$1/simplePush