wrapped functions with sandboxmanager.wrapAsync

dropped "return null"

recipe-client-addon/lib/NormandyDriver.jsm

@@ -159,7 +159,7 @@ this.NormandyDriver = function(sandboxManager) {
     /*
      * Return a promise that resolves to an Addon ID if installation is successful.
      */
-    async installAddon(installUrl) {
+    installAddon: sandboxManager.wrapAsync(async function installAddon(installUrl) {
       const installObj = await AddonManager.getInstallForURL(installUrl, null, "application/x-xpinstall");
       const result = new Promise((resolve, reject) => installObj.addListener({
         onInstallEnded(addonInstall, addon) {
@@ -173,21 +173,20 @@ this.NormandyDriver = function(sandboxManager) {
         },
       }));
       installObj.install();
-      return result;
-    },
+    }),
 
     /*
      * Return a promise that resolves to a success messsage if
      * addon uninstall is successful.
      */
-    async uninstallAddon(addonId) {
+    uninstallAddon: sandboxManager.wrapAsync(async function uninstallAddon(addonId) {
       const addon = await AddonManager.getAddonByID(addonId);
       if (addon === null) {
         throw new Error(`No addon with ID [${addonId}] found.`);
       }
       addon.uninstall();
       return null;
-    },
+    }),
 
     // Sampling
     ratioSample: sandboxManager.wrapAsync(Sampling.ratioSample),