Add a global --registries.d option to skopeo

This is added pretty much only for integration tests right now;
though, it might be useful also for non-root operation.

Also makes a tiny cleanup of contextFromGlobalOptions, removing a
variable.

cmd/skopeo/main.go

@@ -56,6 +56,11 @@ func createApp() *cli.App {
 			Value: "",
 			Usage: "Path to a trust policy file",
 		},
+		cli.StringFlag{
+			Name:  "registries.d",
+			Value: "",
+			Usage: "use registry configuration files in `DIR` (e.g. for docker signature storage)",
+		},
 	}
 	app.Before = func(c *cli.Context) error {
 		if c.GlobalBool("debug") {

cmd/skopeo/utils.go

@@ -8,10 +8,10 @@ import (
 
 // contextFromGlobalOptions returns a types.SystemContext depending on c.
 func contextFromGlobalOptions(c *cli.Context) *types.SystemContext {
-	certPath := c.GlobalString("cert-path")
 	tlsVerify := c.GlobalBool("tls-verify") // FIXME!! defaults to false
 	return &types.SystemContext{
-		DockerCertPath:              certPath,
+		RegistriesDirPath:           c.GlobalString("registries.d"),
+		DockerCertPath:              c.GlobalString("cert-path"),
 		DockerInsecureSkipTLSVerify: !tlsVerify,
 	}
 }

docs/skopeo.1.md

@@ -45,6 +45,8 @@ Most commands refer to container images, using a _transport_`:`_details_ format.
 
   **--policy** _path-to-policy_ Path to a policy.json file to use for verifying signatures and deciding whether an image is trusted, overriding the default trust policy file.
 
+  **--registries.d** _dir_ use registry configuration files in _dir_ (e.g. for docker signature storage), overriding the default path.
+
   **--tls-verify** _bool-value_ Verify certificates
 
   **--help**|**-h** Show help
@@ -139,6 +141,10 @@ show help for `skopeo`
   Default trust policy file, if **--policy** is not specified.
   The policy format is documented in https://github.com/containers/image/blob/master/docs/policy.json.md .
 
+  **/etc/containers/registries.d**
+  Default directory containing registry configuration, if **--registries.d** is not specified.
+  The contents of this directory are documented in https://github.com/containers/image/blob/master/docs/registries.d.md .
+
 # EXAMPLES
 
 ## skopeo copy