Move main.go to repo root folder (elastic#29)

* Move `main.go` to repo root folder

This change simplifies go getting this package by moving `main.go` to
the root folder.

The new command to download this tool will be:

```
go get github.com/elastic/elastic-package
```

This should be the only thing needed by a user that doesn't want to
implement changes to this tool

Makefile

@@ -2,7 +2,7 @@
 
 
 build:
-	go get github.com/elastic/elastic-package/cmd/elastic-package
+	go get github.com/elastic/elastic-package
 
 format:
 	gofmt -s -w .

README.md

@@ -11,7 +11,7 @@ TODO
 Download and build the `elastic-package` binary:
 
 ```bash
-go get github.com/elastic/elastic-package/cmd/elastic-package
+go get github.com/elastic/elastic-package
 ```
 
 Change directory to the integration under development

cmd/elastic-package/build.go → cmd/build.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"github.com/pkg/errors"

cmd/elastic-package/cluster.go → cmd/cluster.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"github.com/pkg/errors"

cmd/root.go

@@ -0,0 +1,19 @@
+package cmd
+
+import (
+	"github.com/spf13/cobra"
+)
+
+// RootCmd creates and returns root cmd for elastic-package
+func RootCmd() *cobra.Command {
+	rootCmd := &cobra.Command{
+		Use:   "elastic-package",
+		Short: "elastic-package - Command line tool for developing Elastic Integrations",
+	}
+	rootCmd.AddCommand(
+		setupClusterCommand(),
+		setupBuildCommand(),
+		setupTestCommand())
+
+	return rootCmd
+}

cmd/elastic-package/testrunner.go → cmd/testrunner.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import "github.com/spf13/cobra"
 

cmd/elastic-package/main.go → main.go

@@ -5,21 +5,13 @@ import (
 	"os"
 
 	"github.com/pkg/errors"
-	"github.com/spf13/cobra"
 
+	"github.com/elastic/elastic-package/cmd"
 	"github.com/elastic/elastic-package/internal/install"
 )
 
 func main() {
-	rootCmd := &cobra.Command{
-		Use:          "elastic-package",
-		Short:        "elastic-package - Command line tool for developing Elastic Integrations",
-		SilenceUsage: true,
-	}
-	rootCmd.AddCommand(
-		setupBuildCommand(),
-		setupClusterCommand(),
-		setupTestCommand())
+	rootCmd := cmd.RootCmd()
 
 	err := install.EnsureInstalled()
 	if err != nil {