WIP: Add new version CentOS X dropping old verions

[junaruga]

This PR is still working in progress. But I decided to share this PR as I need your advises.

The situation is ...

As current exist 7.2.1511-${arch} 's image URLs do not exist except x86_64, those do not work. I updated to latest CentOS 7.6 (or 7.5) image files. Then, x86_64 and armhfp work. But other archs do not work. (docker build -t $repo:$version-iso iso works, but docker run -it --rm $repo:$version-iso ... does not work.)

Here is my repository's result. https://travis-ci.org/junaruga/centos/builds/531571388

Could you give me some advises?

Thank you.

---

Other notable features

• Install libguestfs-tools to use virt-tar-out command from xenial repo. We can not install it from bionic repo because of below error.

  The following packages have unmet dependencies: libguestfs-tools : Depends: libguestfs0 (= 1:1.36.13-1ubuntu3) but it is not going to be installed Depends: libguestfs-perl (= 1:1.36.13-1ubuntu3) but it is not going to be installed E: Unable to correct problems, you have held broken packages.

• Update qemu v3.1.0-3.

• Rafactoring mixed indent with spaces and tab, replacing tab to spaces.

• A bug of virt-tar-out command to convert iso file to tar file? I am asking it to the upstream project here. https://github.com/libguestfs/libguestfs/issues/37

[lafin]

The PR accidentally merged. Please reopen PR.

[junaruga]

@lafin

The PR accidentally merged. Please reopen PR.

I can not reopen this PR. It's not like issue ticket page. It's a specification of GitHub.

You mean that new PR to include a commit that do git revert this PR's commit, right?

[junaruga]

@lafin Ah I understand what you mentioned. You canceled this PR during this PR is being merged to the master branch. This PR is actually not merged to the master branch yet. Sure, I open another PR.