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
Good point, Ben. Yeah, I agree we should tell users what's happening in both README and the output of the `control start` when updating.

I'd vote for leaving the new configuration files/dir in a similar way that RPM handles it (it leaves the *.rpmnew files rather than overwriting configs).