Feat maintain five instances running concurrently

Try to limit a maximum of 5 instances running on the OpenStack. Closes #53 (closed)

Decided to keep different num of images(30) since it takes less resources.

.gitlab-ci.yml

@@ -13,7 +13,7 @@ variables:
   GIT_AUTHOR_NAME: "Gitlab runner"
   GIT_AUTHOR_EMAIL: "gitlab@runner"
   NUM_SERVER_TO_KEEP: 5
-  NUM_IMAGE_TO_KEEP: 30
+  NUM_IMAGE_TO_KEEP: 3
 
 stages:
   - build
@@ -28,6 +28,13 @@ build_image:
   tags:
     - build
   script:
+    - |
+      IMAGE_TO_BE_DELETE=($(openstack image list --sort-column Name --sort-descending -f value -c Name | grep -E '^ood-\d{8}$' | sed -n $(($NUM_IMAGE_TO_KEEP+1))',$p'))
+      for img in $IMAGE_TO_BE_DELETE; do
+        echo ${img} deleted
+      done
+      echo done
+      exit 1
     - |
       if [ ! -d $CI_PROJECT_DIR/CRI_XCBC ]; then
         git clone https://github.com/uabrc/CRI_XCBC.git