add arch var in dockerfile (#8875)

Signed-off-by: bo.jiang <bo.jiang@daocloud.io>

Dockerfile

 # Use imutable image tags rather than mutable tags (like ubuntu:20.04)
 FROM ubuntu:focal-20220316
 
+ARG ARCH=amd64
 ARG TZ=Etc/UTC
 RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
 
@@ -11,7 +12,7 @@ RUN apt update -y \
     && rm -rf /var/lib/apt/lists/*
 RUN curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - \
     && add-apt-repository \
-    "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
+    "deb [arch=$ARCH] https://download.docker.com/linux/ubuntu \
     $(lsb_release -cs) \
     stable" \
     && apt update -y && apt-get install --no-install-recommends -y docker-ce \
@@ -31,6 +32,6 @@ RUN /usr/bin/python3 -m pip install --no-cache-dir pip -U \
     && update-alternatives --install /usr/bin/python python /usr/bin/python3 1
 
 RUN KUBE_VERSION=$(sed -n 's/^kube_version: //p' roles/kubespray-defaults/defaults/main.yaml) \
-    && curl -LO https://storage.googleapis.com/kubernetes-release/release/$KUBE_VERSION/bin/linux/amd64/kubectl \
+    && curl -LO https://storage.googleapis.com/kubernetes-release/release/$KUBE_VERSION/bin/linux/$ARCH/kubectl \
     && chmod a+x kubectl \
     && mv kubectl /usr/local/bin/kubectl