Add nsswitch.conf to our docker image (#4379)

This will cause the alpine images to resolve DNS
using /etc/hosts along with the normal DNS resolver.

Dockerfile

@@ -1,5 +1,7 @@
 FROM alpine:3.5
 
+MAINTAINER Minio Inc <dev@minio.io>
+
 ENV GOPATH /go
 ENV PATH $PATH:$GOPATH/bin
 ENV CGO_ENABLED 0
@@ -9,6 +11,7 @@ WORKDIR /go/src/github.com/minio/
 RUN  \
      apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git go musl-dev && \
+     echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \     
      go get -v -d github.com/minio/minio && \
      cd /go/src/github.com/minio/minio && \
      go install -v -ldflags "$(go run buildscripts/gen-ldflags.go)" && \

Dockerfile.aarch64

@@ -1,5 +1,7 @@
 FROM resin/aarch64-alpine:3.5
 
+MAINTAINER Minio Inc <dev@minio.io>
+
 ENV GOPATH /go
 ENV PATH $PATH:$GOPATH/bin
 ENV CGO_ENABLED 0
@@ -9,6 +11,7 @@ WORKDIR /go/src/github.com/minio/
 RUN  \
      apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git go musl-dev && \
+     echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \     
      go get -v -d github.com/minio/minio && \
      cd /go/src/github.com/minio/minio && \
      go install -v -ldflags "$(go run buildscripts/gen-ldflags.go)" && \

Dockerfile.armhf

@@ -1,5 +1,7 @@
 FROM resin/armhf-alpine:3.5
 
+MAINTAINER Minio Inc <dev@minio.io>
+
 ENV GOPATH /go
 ENV PATH $PATH:$GOPATH/bin
 ENV CGO_ENABLED 0
@@ -9,6 +11,7 @@ WORKDIR /go/src/github.com/minio/
 RUN  \
      apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git go musl-dev && \
+     echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \
      go get -v -d github.com/minio/minio && \
      cd /go/src/github.com/minio/minio && \
      go install -v -ldflags "$(go run buildscripts/gen-ldflags.go)" && \