Modified Makefile to use containerized tools (v2.0.0)

The "build", "install", and "run" targets have been left as-is, and will continue to use the locally installed go.
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-2428 VOL-2647

Change-Id: Iced2839d8e21385c66dd1b8378431af1b966183f
diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..da0158b
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,25 @@
+# Copyright 2020-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+run:
+  modules-download-mode: vendor
+
+linters:
+  enable:
+    #- gochecknoglobals
+    #- gochecknoinits
+    #- gocritic
+    - gofmt
+    #- golint
+    #- unparam