update golang image to eu.gcr.io mirror

Author: kon-angelo

.test-defs/infrastructure-test.yaml

@@ -19,4 +19,4 @@ spec:
     --region="$REGION"
     --tenant-name="$TENANT_NAME"
     --user-name="$USER_NAME"
-  image: golang:1.15.3
+  image: eu.gcr.io/gardener-project/3rd/golang:1.15.5

.test-defs/provider-openstack.yaml

@@ -16,4 +16,4 @@ spec:
     --loadbalancer-provider=$LOADBALANCER_PROVIDER
     --network-worker-cidr=$NETWORK_WORKER_CIDR
 
-  image: golang:1.13.0
+  image: eu.gcr.io/gardener-project/3rd/golang:1.15.5

Dockerfile

@@ -1,12 +1,12 @@
 ############# builder
-FROM golang:1.15.3 AS builder
+FROM eu.gcr.io/gardener-project/3rd/golang:1.15.5 AS builder
 
 WORKDIR /go/src/github.com/gardener/gardener-extension-provider-openstack
 COPY . .
 RUN make install
 
 ############# base
-FROM alpine:3.12.1 AS base
+FROM eu.gcr.io/gardener-project/3rd/alpine:3.12.1 AS base
 
 ############# gardener-extension-provider-openstack
 FROM base AS gardener-extension-provider-openstack