documentation: add instructions for running tests locally (#2006)

CONTRIBUTING.md

@@ -27,6 +27,10 @@ How to get your contributions merged smoothly and quickly.
 - Keep your PR up to date with upstream/master (if there are merge conflicts, we can't really merge your change).
  
 - **All tests need to be passing** before your change can be merged. We recommend you **run tests locally** before creating your PR to catch breakages early on.
+  - `make all` to test everything, OR
+  - `make vet` to catch vet errors
+  - `make test` to run the tests
+  - `make testrace` to run tests in race mode
 
 - Exceptions to the rules can be made if there's a compelling reason for doing so.
  

Makefile

@@ -1,4 +1,4 @@
-all: test testrace
+all: vet test testrace
 
 deps:
 	go get -d -v google.golang.org/grpc/...
@@ -22,6 +22,9 @@ proto:
 	fi
 	go generate google.golang.org/grpc/...
 
+vet:
+	./vet.sh
+
 test: testdeps
 	go test -cpu 1,4 -timeout 5m google.golang.org/grpc/...
 
@@ -39,7 +42,7 @@ clean:
 	updatetestdeps \
 	build \
 	proto \
+	vet \
 	test \
 	testrace \
-	clean \
-	coverage
+	clean