Add Dockerfile to .dockerignore

The Dockerfile is not needed in any of the build targets.
The one exception may be the dev image, however in most cases the docker
source will be bind mounted into the container anyway.

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

.dockerignore

@@ -1,6 +1,8 @@
-bundles
-.gopath
-vendor/pkg
-.go-pkg-cache
+.dockerignore
 .git
+.go-pkg-cache
+.gopath
+bundles
+Dockerfile
+vendor/pkg