Added Dockerfile for redis exporter

Dockerfile.exporter

+FROM alpine:3.9 as builder
+
+ARG EXPORTER_URL="https://github.com/oliver006/redis_exporter/releases/download"
+
+ARG REDIS_EXPORTER_VERSION="1.5.2"
+
+RUN  apk add --no-cache curl ca-certificates && \
+      curl -fL -Lo /tmp/redis_exporter-v${REDIS_EXPORTER_VERSION}.linux-amd64.tar.gz \
+      ${EXPORTER_URL}/${REDIS_EXPORTER_VERSION}/redis_exporter-v${REDIS_EXPORTER_VERSION}.linux-amd64.tar.gz && \
+      cd /tmp && tar -xvzf redis_exporter-v${REDIS_EXPORTER_VERSION}.linux-amd64.tar.gz && \
+      mv redis_exporter-v${REDIS_EXPORTER_VERSION}.linux-amd64 redis_exporter
+
+FROM scratch:latest
+
+MAINTAINER Opstree Solutions
+
+LABEL VERSION=1.0 \
+      ARCH=AMD64 \
+      DESCRIPTION="A production grade redis exporter docker image created by Opstree Solutions"
+
+COPY --from=builder /etc/ssl/certs /etc/ssl/certs
+COPY --from=builder /tmp/redis_exporter/redis_exporter /usr/local/bin/redis_exporter
+
+USER non-root
+
+EXPOSE 9121
+
+ENTRYPOINT ["/usr/local/bin/redis_exporter"]