VM should have 8 cores to make build faster in GCloud.
To get rid of ssfs between build hosts the build step
and upgrade test step are separated as well as
repository discriåtion generation
We do not build RHEL packageas, but create RHEL repos as symlinks
to CentOS repos. For RHEL8 was an expection intruduced, because
CentOS 8 was not available at the time when RHEL8 was released.
Now CentOS 8 is also available, switching to CentOS 8 image.
During the build first binary packages are generated and copied into
'pre-repo' direcotory. Then binary repository is created and next
step is to copy repository into final directory according agreed
binary repo sirectories structure. After it temparal direcotries
are not needed.
