[VOL-1920] Migrated voltha-go from dep to go mod for dependency management

Change-Id: Ie14418cef7ba046a7c43a343b9017c436af6b395
diff --git a/Makefile b/Makefile
index f92780c..c2a5e0a 100644
--- a/Makefile
+++ b/Makefile
@@ -40,6 +40,13 @@
 DOCKER_LABEL_BUILD_DATE    ?= $(shell date -u "+%Y-%m-%dT%H:%M:%SZ")
 DOCKER_LABEL_COMMIT_DATE   = $(shell git show -s --format=%cd --date=iso-strict HEAD)
 
+# Default is GO111MODULE=auto, which will refuse to use go mod if running
+# go less than 1.13.0 and this repository is checked out in GOPATH. For now,
+# force module usage. This affects commands executed from this Makefile, but
+# not the environment inside the Docker build (which does not build from
+# inside a GOPATH).
+export GO111MODULE=on
+
 DOCKER_BUILD_ARGS ?= \
 	${DOCKER_EXTRA_ARGS} \
 	--build-arg org_label_schema_version="${VERSION}" \
@@ -73,7 +80,7 @@
 	@echo "lint-dockerfile      : Perform static analysis on Dockerfiles"
 	@echo "lint-style           : Verify code is properly gofmt-ed"
 	@echo "lint-sanity          : Verify that 'go vet' doesn't report any issues"
-	@echo "lint-dep             : Verify the integrity of the 'dep' files"
+	@echo "lint-mod             : Verify the integrity of the 'mod' files"
 	@echo "lint                 : Shorthand for lint-style & lint-sanity"
 	@echo "test                 : Generate reports for all go tests"
 	@echo
@@ -168,15 +175,15 @@
 
 lint-sanity:
 	@echo "Running sanity check..."
-	@go vet ./...
+	@go vet -mod=vendor ./...
 	@echo "Sanity check OK"
 
-lint-dep:
+lint-mod:
 	@echo "Running dependency check..."
-	@dep check
+	@go mod verify
 	@echo "Dependency check OK"
 
-lint: lint-style lint-sanity lint-dep lint-dockerfile
+lint: lint-style lint-sanity lint-mod lint-dockerfile
 
 # Rules to automatically install golangci-lint
 GOLANGCI_LINT_TOOL?=$(shell which golangci-lint)
@@ -217,7 +224,7 @@
 
 test: go_junit_install gocover_cobertura_install
 	@mkdir -p ./tests/results
-	@go test -v -coverprofile ./tests/results/go-test-coverage.out -covermode count ./... 2>&1 | tee ./tests/results/go-test-results.out ;\
+	@go test -mod=vendor -v -coverprofile ./tests/results/go-test-coverage.out -covermode count ./... 2>&1 | tee ./tests/results/go-test-results.out ;\
 	RETURN=$$? ;\
 	$(GO_JUNIT_REPORT) < ./tests/results/go-test-results.out > ./tests/results/go-test-results.xml ;\
 	$(GOCOVER_COBERTURA) < ./tests/results/go-test-coverage.out > ./tests/results/go-test-coverage.xml ;\