Dockerfile: upgrade base image to alpine 3.10 (#1178)

The 3.5 images are not maintained by upstream anymore, and 3.10 is
the latest stable branch.

images/tidb-operator-e2e/Dockerfile

@@ -3,20 +3,20 @@ FROM golang:1.10-alpine AS builder
 
 # Uncomment these lines to hack the repositories
 # RUN echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.3/main" > /etc/apk/repositories  && \
-#    echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.5/community" >> /etc/apk/repositories
+#    echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.10/community" >> /etc/apk/repositories
 
 RUN apk update && apk add --no-cache git
 RUN go get github.com/onsi/ginkgo/ginkgo
 
 # Executable image
-FROM alpine:3.5
+FROM alpine:3.10
 
 ENV KUBECTL_VERSION=v1.10.2
 ENV HELM_VERSION=v2.9.1
 
 # Uncomment these lines to hack the repositories
 # RUN echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.3/main" > /etc/apk/repositories  && \
-#    echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.5/community" >> /etc/apk/repositories
+#    echo "https://mirrors.tuna.tsinghua.edu.cn/alpine/v3.10/community" >> /etc/apk/repositories
 
 RUN apk update && apk add --no-cache ca-certificates curl
 

images/tidb-operator/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.5
+FROM alpine:3.10
 
 RUN apk add tzdata --no-cache
 ADD bin/tidb-scheduler /usr/local/bin/tidb-scheduler

tests/images/e2e/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.5
+FROM alpine:3.10
 
 ENV KUBECTL_VERSION=v1.12.2
 ENV HELM_VERSION=v2.9.1

tests/images/stability-test/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.5
+FROM alpine:3.10
 
 ENV KUBECTL_VERSION=v1.12.2
 ENV HELM_VERSION=v2.9.1

tests/images/test-apiserver/Dockerfile

@@ -1,3 +1,3 @@
-FROM alpine:3.5
+FROM alpine:3.10
 
 ADD bin/tidb-apiserver /usr/local/bin/tidb-apiserver