Fix docker files after hadolint check

Dockerfile

@@ -1,21 +1,21 @@
 FROM golang:alpine as builder
 
-ADD . /usr/src/sriov-cni
+COPY . /usr/src/sriov-cni
 
 ENV HTTP_PROXY $http_proxy
 ENV HTTPS_PROXY $https_proxy
 
-RUN apk add --update --virtual build-dependencies build-base linux-headers && \
-    cd /usr/src/sriov-cni && \
+WORKDIR /usr/src/sriov-cni
+RUN apk add --no-cache --virtual build-dependencies build-base=~0.5 && \
     make clean && \
     make build
 
-FROM alpine
+FROM alpine:3
 COPY --from=builder /usr/src/sriov-cni/build/sriov /usr/bin/
 WORKDIR /
 
 LABEL io.k8s.display-name="SR-IOV CNI"
 
-ADD ./images/entrypoint.sh /
+COPY ./images/entrypoint.sh /
 
 ENTRYPOINT ["/entrypoint.sh"]

Dockerfile.rhel7

@@ -1,6 +1,6 @@
 FROM registry.svc.ci.openshift.org/ocp/builder:golang-1.10 AS builder
 
-ADD . /usr/src/sriov-cni
+COPY . /usr/src/sriov-cni
 
 WORKDIR /usr/src/sriov-cni
 RUN make clean && \
@@ -12,6 +12,6 @@ WORKDIR /
 
 LABEL io.k8s.display-name="SR-IOV CNI"
 
-ADD ./images/entrypoint.sh /
+COPY ./images/entrypoint.sh /
 
 ENTRYPOINT ["/entrypoint.sh"]