Cleanup Docker context and decrease build time

This is based off the work found in kubernetes-sigs#1307 that was never merged. It
moves around the install and copy of certain conponents to take better
advantage of the Docker cache ad well as drops running tests during the
build of the image.

The reason for dropping tests is to improve build time and as running
tests within the build while they're already being run in CI seems like
an unnecessary added tax.

Signed-off-by: Danny Grove <danny@drgrovellc.com>

.dockerignore

@@ -0,0 +1,14 @@
+# Git Related Items
+.git
+.github
+.gitignore
+
+# CI Related Items
+.travis.yml
+cloudbuild.yaml
+.golangci.yml
+.zappr.yaml
+
+# Other
+docs
+OWNERS

Dockerfile

@@ -19,10 +19,13 @@ ARG VERSION
 
 WORKDIR /sigs.k8s.io/external-dns
 
-COPY . .
+COPY go.mod .
+COPY go.sum .
 RUN go mod vendor && \
-    make test && \
-    make build
+    go mod download
+
+COPY . .
+RUN make build
 
 # final image
 FROM alpine:3.11.5

Dockerfile.mini

@@ -16,13 +16,18 @@ FROM golang:1.14 as builder
 
 WORKDIR /sigs.k8s.io/external-dns
 
+RUN apt-get update \
+    && apt-get install \
+        ca-certificates \
+    && update-ca-certificates
+
+COPY go.mod .
+COPY go.sum .
+RUN go mod vendor && \
+    go mod download
+
 COPY . .
-RUN apt-get update && \
-    apt-get install ca-certificates && \
-    update-ca-certificates && \
-    go mod vendor && \
-    make test && \
-    make build
+RUN make build
 
 FROM gcr.io/distroless/static