Updated tools version to 2.0.0

Also merged lint-style (gofmt) into golangci-lint (enabled gofmt).
Also removed redundant lint-sanity (govet) which is already checked by golangci-lint.
Also made minor code changes to pass new golangci-lint tests.
Also changed lint-mod slightly so it reverts any changes it makes go.mod, go.sum, and vendor/.

VOL-2647

Change-Id: I15557edf0f9225ea1c44e5bab29481d17a82e2b8
diff --git a/go.mod b/go.mod
index 12a6664..9888abb 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/opencord/voltha-go
 
-go 1.12
+go 1.13
 
 require (
 	github.com/gogo/protobuf v1.3.0