Fix linting issues and update make lint target.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

Dockerfile

@@ -1,3 +1,5 @@
+ARG GOLANG_CI_LINT_VERSION
+
 FROM golang:1.18 as builder
 ENV PATH /go/bin:/usr/local/go/bin:$PATH
 ENV GOPATH /go
@@ -7,6 +9,22 @@ ARG BUILD_TAGS=""
 RUN make VK_BUILD_TAGS="${BUILD_TAGS}" build
 RUN cp bin/virtual-kubelet /usr/bin/virtual-kubelet
 
+FROM golangci/golangci-lint:${GOLANG_CI_LINT_VERSION} as lint
+WORKDIR /app
+COPY go.mod ./
+COPY go.sum ./
+RUN \
+    --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    go mod download
+COPY . .
+ARG OUT_FORMAT
+RUN \
+    --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/golangci-lint \
+    golangci-lint run -v $(if [ -n "${OUT_FORMAT}" ]; then echo "--out-format=${OUT_FORMAT}"; fi)
+
 FROM scratch
 COPY --from=builder /usr/bin/virtual-kubelet /usr/bin/virtual-kubelet
 COPY --from=builder /etc/ssl/certs/ /etc/ssl/certs