Internals: Switch to v2 go.mod, drop GOPATH, and fix Azure Pipelines (#595)

* Switched to v2 go.mod

Also set GO111MODULE=on in build stuff to always use Go modules
even when in GOPATH.

* Ensure go.mod, go.sum, and vendor are up to date

* Attempt to fix Azure pipelines

* Add set -e to properly fail on exit (it didn't seem to be
  propagating properly before).
* Set workingDirectory for GoFmt and GoGen (this might be why it
  fails unlike compile and unitests).

* Another attempt to fix Azure Pipelines

* Use the Go env template for all go-related jobs.

* Completely fixed Azure Pipelines

* Added a display name to GoFmt for consistency.
* Fixed diffs for GoFmt and GoGen.
* Show git status for checks.

* Drop GOPATH for tests

TODO: Do the same for integration tests.

* Drop GOPATH for integration tests

* Show more diffs

* Regenerate provider support matrix

This wasn't done in #590...

build/build.go

@@ -17,12 +17,13 @@ var goos = flag.String("os", "", "OS to build (linux, windows, or darwin) Defaul
 func main() {
 	flag.Parse()
 	flags := fmt.Sprintf(`-s -w -X main.SHA="%s" -X main.BuildTime=%d`, getVersion(), time.Now().Unix())
-	pkg := "github.com/StackExchange/dnscontrol"
+	pkg := "github.com/StackExchange/dnscontrol/v2"
 
 	build := func(out, goos string) {
 		log.Printf("Building %s", out)
 		cmd := exec.Command("go", "build", "-o", out, "-ldflags", flags, pkg)
 		os.Setenv("GOOS", goos)
+		os.Setenv("GO111MODULE", "on")
 		cmd.Stderr = os.Stderr
 		cmd.Stdout = os.Stdout
 		err := cmd.Run()