Implement verify_recovery for systemimage:install

Option as specified in ubports/installer-configs#178

Example:

```yml
- systemimage:install:
    verify_recovery: true
```

src/core/plugins/systemimage/plugin.js

@@ -30,7 +30,7 @@ class SystemimagePlugin extends Plugin {
    * systemimage:install action
    * @returns {Promise<Array<Object>>}
    */
-  action__install() {
+  action__install({ verify_recovery } = {}) {
     return api
       .getImages(
         this.props.settings.channel,
@@ -56,6 +56,16 @@ class SystemimagePlugin extends Plugin {
             {
               "adb:wait": null
             },
+            ...(verify_recovery
+              ? [
+                  {
+                    "adb:assert_prop": {
+                      prop: "ro.ubuntu.recovery",
+                      value: "true"
+                    }
+                  }
+                ]
+              : []),
             {
               "adb:preparesystemimage": null
             },

src/core/plugins/systemimage/plugin.spec.js

@@ -19,8 +19,8 @@ beforeEach(() => jest.clearAllMocks());
 
 describe("systemimage plugin", () => {
   describe("actions", () => {
-    describe("download", () => {
-      it("should create download steps", () =>
+    describe("install", () => {
+      it("should create install actions", () =>
         systemimage.action__install().then(r => {
           expect(r).toHaveLength(1);
           expect(r[0].actions).toHaveLength(5);
@@ -49,6 +49,14 @@ describe("systemimage plugin", () => {
             }
           });
         }));
+      it("should verify recovery", () =>
+        systemimage.action__install({ verify_recovery: true }).then(r => {
+          expect(r).toHaveLength(1);
+          expect(r[0].actions).toHaveLength(6);
+          expect(r[0].actions).toContainEqual({
+            "adb:assert_prop": { prop: "ro.ubuntu.recovery", value: "true" }
+          });
+        }));
     });
   });
   describe("remote_values", () => {