Allow specifying release channel when signing

Fixes mozilla#248

src/amo-client.js

@@ -77,12 +77,13 @@ export class Client {
    *   - `xpiPath` Path to xpi file.
    *   - `guid` Optional add-on GUID, aka the ID in install.rdf.
    *   - `version` add-on version string.
+   *   - `channel` release channel (listed, unlisted).
    * @return {Promise} signingResult with keys:
    *   - success: boolean
    *   - downloadedFiles: Array of file objects
    *   - id: string identifier for the signed add-on
    */
-  sign({guid, version, xpiPath}) {
+  sign({channel=null, guid, version, xpiPath}) {
 
     const formData = {
       upload: this._fs.createReadStream(xpiPath),
@@ -93,6 +94,9 @@ export class Client {
       // PUT to a specific URL for this add-on + version.
       addonUrl += encodeURIComponent(guid) +
         "/versions/" + encodeURIComponent(version) + "/";
+      if (channel) {
+        formData.channel = channel;
+      }
     } else {
       // POST to a generic URL to create a new add-on.
       this.debug("Signing add-on without an ID");

src/index.js

@@ -14,6 +14,9 @@ export default function signAddon(
     id,
     // The add-on version number for AMO.
     version,
+    // The release channel on AMO.
+    // Missing or invalid translates to most recently used channel.
+    channel=null,
     // Your API key (JWT issuer) from AMO Devhub.
     apiKey,
     // Your API secret (JWT secret) from AMO Devhub.
@@ -87,6 +90,7 @@ export default function signAddon(
         xpiPath: xpiPath,
         guid: id,
         version: version,
+        channel,
       });
 
     });