Include architecture name in built ISO files

Since x64 builds are stable enough to test in virtual machines (and even in some real hardware), it makes important to test them often along with x86 builds and report their specific bugs.

However there is one little problem that makes testing a bit more difficult. ISO/CD image files always have the same name for all architectures when built from source. When you are testing them in VirtualBox (even in two separate VMs), previously attached ISO files are being memorized by the software, and you have this picture:

So which one of these files are for x86 architecture, and which one are for x64? That is the question.

It would be better to append architecture name to the built ISO files, like bootcd-x86.iso / livecd-x86.iso and bootcd-x64.iso / livecd-x64.iso. Someday we will support more architectures like arm and arm64, and this problem will be even more noticeable.

Of course, renaming the ISO files would require updating our build system scripts (both Buildbot and GitHub Actions CI).