Warn when hostname already taken on bluemix

[hughesj]

When you select the Bluemix button, the hostname on bluemix is going to be `http://<the name of the project>.eu-gb.mybluemix.net/myLibertyApp/. If that's already taken (by someone else) then the maven build will fail with :

[INFO] Creating application 'LibertyProject'
[WARNING] POST request for "https://api.eu-gb.bluemix.net/v2/routes" resulted in 400 (Bad Request); invoking error handler
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 21.098 s
[INFO] Finished at: 2016-12-14T14:36:48+00:00
[INFO] Final Memory: 31M/51M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.cloudfoundry:cf-maven-plugin:1.1.3:push (push) on project myArtifactId: Error while creating application 'LibertyProject'. Error message: '400 Bad Request'. Description: 'The host is taken: LibertyProject' -> [Help 1]