Move load of kms to main package.

With this change packages that import the authority won't load by
default all the supported kms with all its dependencies.

Fixes #228

cmd/step-ca/main.go

@@ -23,6 +23,14 @@ import (
 	"github.com/smallstep/cli/config"
 	"github.com/smallstep/cli/usage"
 	"github.com/urfave/cli"
+
+	// Enabled kms interfaces.
+	_ "github.com/smallstep/certificates/kms/awskms"
+	_ "github.com/smallstep/certificates/kms/cloudkms"
+	_ "github.com/smallstep/certificates/kms/softkms"
+
+	// Experimental kms interfaces.
+	_ "github.com/smallstep/certificates/kms/yubikey"
 )
 
 // commit and buildTime are filled in during build by the Makefile

cmd/step-yubikey-init/main.go

@@ -22,6 +22,9 @@ import (
 	"github.com/smallstep/cli/crypto/pemutil"
 	"github.com/smallstep/cli/ui"
 	"github.com/smallstep/cli/utils"
+
+	// Enable yubikey.
+	_ "github.com/smallstep/certificates/kms/yubikey"
 )
 
 type Config struct {

kms/kms.go

@@ -7,13 +7,8 @@ import (
 	"github.com/pkg/errors"
 	"github.com/smallstep/certificates/kms/apiv1"
 
-	// Enabled kms interfaces.
-	_ "github.com/smallstep/certificates/kms/awskms"
-	_ "github.com/smallstep/certificates/kms/cloudkms"
+	// Enable default implementation
 	_ "github.com/smallstep/certificates/kms/softkms"
-
-	// Experimental kms interfaces.
-	_ "github.com/smallstep/certificates/kms/yubikey"
 )
 
 // KeyManager is the interface implemented by all the KMS.