Separate enabling buildkit (and installing buildx) and gcr mirror

.travis.yml

@@ -18,8 +18,11 @@ before_install:
 
   # enable buildkit plus configure gcr mirror
   #- sh hack/enable-docker-buildkit.sh
-  #- sudo service docker restart || (systemctl status docker.service; journalctl -xe)
+  - sh hack/use-gcr-mirror.sh
+  - sudo service docker restart || (systemctl status docker.service; journalctl -xe)
   - docker info
+
+  # Remove buildkit'isms from Dockerfiles
   - sh hack/strip-buildkitisms.sh
 
 install: 

hack/enable-docker-buildkit.sh

@@ -9,19 +9,15 @@ if [ -f /etc/docker/daemon.json ]; then
     # avoid `jq ... | sudo tee /etc/docker/daemon.json` as we were
     # having 0-byte files created instead (!)
     jq '.+{"experimental":true}' /etc/docker/daemon.json \
-    | jq '."registry-mirrors" -= ["https://registry.docker.io"]' \
-    | jq '."registry-mirrors" += ["https://mirror.gcr.io"]' \
     | tee /tmp/docker-daemon.json
-    echo "/tmp/docker-daemon.json:"
-    sed 's/^/> /' /tmp/docker-daemon.json
     sudo cp /tmp/docker-daemon.json /etc/docker/daemon.json
 
     echo "/etc/docker/daemon.json now:"
     sed 's/^/> /' /etc/docker/daemon.json
 else
     sudo mkdir -vp /etc/docker
     echo "/etc/docker/daemon.json now:"
-    echo '{"experimental":true,"registry-mirrors":["https://mirror.gcr.io"]}' \
+    echo '{"experimental":true}' \
     | sudo tee /etc/docker/daemon.json
 fi
 

hack/use-gcr-mirror.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+echo ">> enabling gcr mirror"
+if [ -f /etc/docker/daemon.json ]; then
+    echo "/etc/docker/daemon.json was:"
+    sed 's/^/> /' /etc/docker/daemon.json
+
+    # avoid `jq ... | sudo tee /etc/docker/daemon.json` as we were
+    # having 0-byte files created instead (!)
+    cat /etc/docker/daemon.json \
+    | jq '."registry-mirrors" -= ["https://registry.docker.io"]' \
+    | jq '."registry-mirrors" += ["https://mirror.gcr.io"]' \
+    | tee /tmp/docker-daemon.json
+    sudo cp /tmp/docker-daemon.json /etc/docker/daemon.json
+
+    echo "/etc/docker/daemon.json now:"
+    sed 's/^/> /' /etc/docker/daemon.json
+else
+    sudo mkdir -vp /etc/docker
+    echo "/etc/docker/daemon.json now:"
+    echo '{"registry-mirrors":["https://mirror.gcr.io"]}' \
+    | sudo tee /etc/docker/daemon.json
+fi
+