Move .coverage.sh to make coverage (#301)

This fix moves the content of `.coverage.sh` to the Makefile
and creates a target of `make coverage`. This cleans up as
there is really no need to have a redundant script for
simple coverage test.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Makefile

@@ -38,6 +38,18 @@ testk8s: deps
 testk8s-setup: deps
 	go test -v ./middleware/kubernetes/... -run TestKubernetes
 
+.PHONY: coverage
+coverage: deps
+	set -e -x
+	echo "" > coverage.txt
+	for d in `go list ./... | grep -v vendor`; do \
+		go test -race -coverprofile=profile.out -covermode=atomic $$d; \
+		if [ -f profile.out ]; then \
+			cat profile.out >> coverage.txt; \
+			rm profile.out; \
+		fi; \
+	done
+
 .PHONY: clean
 clean:
 	go clean