Make more intelligent use of the cache

Bust cache on the dynamic files
Use the cached builds for both virtualbox and Hyper-V
Hopefully improve loop downloading files to cache

.gitlab-ci.yml

@@ -10,6 +10,10 @@ variables:
 
 generate:
   stage: generate
+  cache:
+    - key: isofiles
+      paths:
+        - cache/*.iso
   artifacts:
     paths:
       - distros/**/*.pkrvars.hcl
@@ -78,7 +82,9 @@ downloads:
       for vars in $(find distros/ -name '*.pkrvars.hcl'); do
         file=$(echo var.iso.url | packer console -var-file=${vars} -config-type=hcl2 sources/)
         base="$(basename "${file}")"
-        if [ ! -e "cache/${base}" ]; then
+        if [ -e "cache/${base}" ]; then
+          echo "Cached file already exists"
+        else
           files+=("-O" "${file}")
         fi
       done