Build static in dockerfile

Change-Id: I2b16196ab0a4aa96227418596888cd1745e06367
diff --git a/Dockerfile b/Dockerfile
index 54afae3..888f40e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -12,7 +12,9 @@
 
 RUN go test .
 
-RUN go build -o /src/kalamar-plugin-externalresources .
+RUN STATIC="-extldflags '-static'" \
+    STATICENV="CGO_ENABLED=0 GOOS=linux GOARCH=amd64" \
+    go build -o /src/kalamar-plugin-externalresources .
 
 # Main stage
 FROM busybox:glibc