Split Terraform OSS and enterprise test suites

[hugoShaka]

This PR does 3 changes:

• splits the Terraform tests in two test suites:
  • TerraformSuiteOSS
  • TerraformSuiteEnterprise
• makes the test suites exported so they can be run from teleport.e
• makes the enterprise tests fail when running against a non-enterprise Teleport

[hugoShaka]

Once this PR is approved, I will add the following code into e/integration/helpers.go

package integration

import (
	"testing"

	"github.com/stretchr/testify/require"

	eauth "github.com/gravitational/teleport/e/lib/auth"
	"github.com/gravitational/teleport/lib/plugin"
)

func GetTestAuthPlugin(t *testing.T) plugin.Plugin {
	p, err := eauth.NewPlugin(eauth.Config{
		License: eauth.ValidLicense{},
	})
	require.NoError(t, err)
	return p
}

[marcoandredinis]

I would drop all the OSS references.
I think it would be simpler if we had TerraformSuite and TerraformSuiteEnterprise