[System Tests] Fix open source system tests CI (#1071)

.github/workflows/system-tests-opensource.yml

@@ -42,7 +42,7 @@ jobs:
   run-system-tests-opensource-ci:
     timeout-minutes: 60
     name: Run System Tests Open Source
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     # let's not run this on every fork, change to your fork when developing
     if: github.repository == 'mlrun/mlrun' || github.event_name == 'workflow_dispatch'
@@ -130,10 +130,10 @@ jobs:
       with:
         version: "v3.3.4"
 
-    - uses: manusa/actions-setup-minikube@v2.3.0
+    - uses: manusa/actions-setup-minikube@v2.4.2
       with:
         minikube version: "v1.15.1"
-        kubernetes version: "v1.17.5"
+        kubernetes version: "v1.17.9"
         driver: docker
         github token: ${{ github.token }}
         start args: '--addons registry'
@@ -142,11 +142,11 @@ jobs:
       run: |
         helm repo add v3io-stable https://v3io.github.io/helm-charts/stable
         helm repo update
-        kubectl create namespace ${NAMESPACE}
+        minikube kubectl -- create namespace ${NAMESPACE}
 
     - name: Override MLRun Registry ConfigMap
       run: |
-        cat <<EOF | kubectl apply -f -
+        cat <<EOF | minikube kubectl -- apply -f -
         apiVersion: v1
         kind: ConfigMap
         metadata: