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 changed lint-mod slightly so it reverts any changes it makes go.mod, go.sum, and vendor/.

VOL-2647

Change-Id: I0da8f5db28116efaa4958dc8778ffa0e851d6640
diff --git a/VERSION b/VERSION
index e265a8c..4d92398 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-3.0.15
+3.0.16-dev