Use "Ubuntu 18.04", not "Ubuntu Bionic" at Create a New Instance

#1

When you create a new instance, you select the Linux distribution and then the version.
For Ubuntu, the LTS versions appear as “Bionic”, “Xenial” and “Trusty”.

In terms of usability and simplicity, I believe these should be instead “Ubuntu 18.04”, “Ubuntu 16.04” and “Ubuntu 14.04”.

The codenames are not meant to be used in that way. The official release version should be shown instead.