Use Debian go image in Dockerfile

The build needs bash in order to process build tags correctly. Alpine
doesn't come with bash... Debian comes with all the things we need out
of the box, so let's just use that.

Dockerfile

@@ -1,25 +1,12 @@
-FROM golang:alpine as builder
-
+FROM golang:1.12 as builder
 ENV PATH /go/bin:/usr/local/go/bin:$PATH
 ENV GOPATH /go
-
-RUN apk add --no-cache \
-	ca-certificates \
-	--virtual .build-deps \
-	git \
-	gcc \
-	libc-dev \
-	libgcc \
-	make \
-	bash
-
 COPY . /go/src/github.com/virtual-kubelet/virtual-kubelet
 WORKDIR /go/src/github.com/virtual-kubelet/virtual-kubelet
 ARG BUILD_TAGS="netgo osusergo"
 RUN make VK_BUILD_TAGS="${BUILD_TAGS}" build
 RUN cp bin/virtual-kubelet /usr/bin/virtual-kubelet
 
-
 FROM scratch
 COPY --from=builder /usr/bin/virtual-kubelet /usr/bin/virtual-kubelet
 COPY --from=builder /etc/ssl/certs/ /etc/ssl/certs