fix(@angular-devkit/architect): always clear TestProjectHost on restore

Author: filipesilva

packages/angular_devkit/architect/testing/test-project-host.ts

@@ -18,7 +18,7 @@ import {
 import { NodeJsSyncHost } from '@angular-devkit/core/node';
 import { Stats } from 'fs';
 import { EMPTY, Observable, from, of } from 'rxjs';
-import { concatMap, delay, map, mergeMap, retry, tap } from 'rxjs/operators';
+import { concatMap, delay, finalize, map, mergeMap, retry, tap } from 'rxjs/operators';
 
 
 export class TestProjectHost extends NodeJsSyncHost {
@@ -90,13 +90,12 @@ export class TestProjectHost extends NodeJsSyncHost {
     // Wait 50ms and retry up to 10 times, to give time for file locks to clear.
     return this.exists(this.root()).pipe(
       delay(50),
-      concatMap(exists => exists ? this.delete(this.root()) : of(null)),
+      concatMap(exists => exists ? this.delete(this.root()) : EMPTY),
       retry(10),
-      tap(() => {
+      finalize(() => {
         this._currentRoot = null;
         this._scopedSyncHost = null;
       }),
-      map(() => { }),
     );
   }