Set cpu cores number to build VM and separate build and upgrade

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

BUILD/mdbci/copy_repos.sh

@@ -69,5 +69,3 @@ cd $dir
 
 echo "cleaning ${unsorted_repo_dir}/$target/$box"
 rm -rf ${unsorted_repo_dir}/$target/$box
-
-${mdbci_dir}/mdbci generate-product-repositories --product maxscale_ci --product-version $target