build: Remove vendor-grepping from Makefile

As of Go 1.9, ./... excludes the vendor directory by default and so we
no longer need to jump through hoops to exclude vendored packages from
testing, vetting, etc.

As a simplification this also re-introduces builtin/bins to the set of
packages we run tests on. With the providers now split into their own
repositories there's far fewer of these and so including them doesn't
really hurt anything, and makes our invocations here simpler.

Makefile

@@ -1,4 +1,4 @@
-TEST?=$$(go list ./... | grep -v '/terraform/vendor/' | grep -v '/builtin/bins/')
+TEST?=./...
 GOFMT_FILES?=$$(find . -name '*.go' | grep -v vendor)
 
 default: test vet
@@ -27,10 +27,11 @@ plugin-dev: generate
 	mv $(GOPATH)/bin/$(PLUGIN) $(GOPATH)/bin/terraform-$(PLUGIN)
 
 # test runs the unit tests
+# we run this one package at a time here because running the entire suite in
+# one command creates memory usage issues when running in Travis-CI.
 test: fmtcheck generate
 	go test -i $(TEST) || exit 1
-	echo $(TEST) | \
-		xargs -t -n4 go test $(TESTARGS) -timeout=60s -parallel=4
+	go list $(TEST) | xargs -t -n4 go test $(TESTARGS) -timeout=60s -parallel=4
 
 # testacc runs acceptance tests
 testacc: fmtcheck generate
@@ -64,8 +65,8 @@ cover:
 # vet runs the Go source code static analysis tool `vet` to find
 # any common errors.
 vet:
-	@echo 'go vet $$(go list ./... | grep -v /terraform/vendor/)'
-	@go vet $$(go list ./... | grep -v /terraform/vendor/) ; if [ $$? -eq 1 ]; then \
+	@echo 'go vet ./...'
+	@go vet ./... ; if [ $$? -eq 1 ]; then \
 		echo ""; \
 		echo "Vet found suspicious constructs. Please check the reported constructs"; \
 		echo "and fix them if necessary before submitting the code for review."; \
@@ -78,7 +79,7 @@ generate:
 	@which stringer > /dev/null; if [ $$? -ne 0 ]; then \
 	  go get -u golang.org/x/tools/cmd/stringer; \
 	fi
-	go generate $$(go list ./... | grep -v /terraform/vendor/)
+	go generate ./...
 	@go fmt command/internal_plugin_list.go > /dev/null
 
 fmt: