Fix modified go.sum issue in beat generators

There were two issues:

`go mod download` was run after the newly generated beat was committed. This modified the go.sum because it
adds hashes for the downloaded dependencies. The caused `mage check` to fail because the git project has
pending changes.

The dependencies of package_test.go were missing from go.sum. When running `mage testPackages` it
was failing because github.com/blakesmith/ar and github.com/cavaliercoder/go-rpm were missing.

generator/_templates/beat/{beat}/tools/tools.go

@@ -6,12 +6,13 @@
 package tools
 
 import (
+	_ "github.com/blakesmith/ar"
+	_ "github.com/cavaliercoder/go-rpm"
 	_ "github.com/magefile/mage"
+	_ "github.com/mitchellh/gox"
 	_ "github.com/pierrre/gotestcover"
 	_ "github.com/tsg/go-daemon"
+	_ "golang.org/x/lint/golint"
 	_ "golang.org/x/tools/cmd/goimports"
 	_ "gotest.tools/gotestsum/cmd"
-
-	_ "github.com/mitchellh/gox"
-	_ "golang.org/x/lint/golint"
 )

generator/_templates/metricbeat/{beat}/tools/tools.go

@@ -6,12 +6,13 @@
 package tools
 
 import (
+	_ "github.com/blakesmith/ar"
+	_ "github.com/cavaliercoder/go-rpm"
 	_ "github.com/magefile/mage"
+	_ "github.com/mitchellh/gox"
 	_ "github.com/pierrre/gotestcover"
 	_ "github.com/tsg/go-daemon"
+	_ "golang.org/x/lint/golint"
 	_ "golang.org/x/tools/cmd/goimports"
 	_ "gotest.tools/gotestsum/cmd"
-
-	_ "github.com/mitchellh/gox"
-	_ "golang.org/x/lint/golint"
 )

generator/common/Makefile

@@ -22,8 +22,6 @@ test: prepare-test
 test-package: test
 	cd ${BEAT_PATH} ; \
 	export PATH=$${GOPATH}/bin:$${PATH}; \
-	go mod tidy && \
-	go mod download all && \
 	mage package
 
 .PHONY: prepare-test

generator/common/beatgen/beatgen.go

@@ -126,6 +126,16 @@ func Generate() error {
 		return errors.Wrap(err, "error while getting required beats version")
 	}
 
+	// After fully populating go.mod download the deps to set the hashes
+	// within the go.sum.
+	if err = gotool.Mod.Download(); err != nil {
+		return errors.Wrap(err, "failed to download go.mod deps")
+	}
+	// Finally, cleanup any formatting issues in the go.mod/go.sum.
+	if err = gotool.Mod.Tidy(); err != nil {
+		return errors.Wrap(err, "error running 'go mod tidy'")
+	}
+
 	mg.Deps(setup.GitInit)
 
 	if cfg["type"] == "metricbeat" {