Fix #11 - Make minor/milestone version updates easier

- Remove Vert.x minor/milestone version from the cartridge metadata
- Update setup/install/control scripts
- Update README, improve Updating Vert.x steps

https://github.com/vert-x/openshift-cartridge/issues/11
https://bugzilla.redhat.com/show_bug.cgi?id=1158736
Yea probably should add something to the README which addresses this.