fix: get_app_container returns non-existent path

In case application is not installed on simulator, `xcrun simctl get_app_container ...` command returns some random path that does not exist. In case you install the application after that, the path is not the same as the returned by the command before that.
So check if the path exists and return null in case it does not.

Author: rosen-vladimirov

lib/simctl.ts

@@ -2,6 +2,7 @@ import childProcess = require("./child-process");
 import * as child_process from "child_process";
 import errors = require("./errors");
 import * as _ from "lodash";
+import * as fs from "fs";
 
 export class Simctl implements ISimctl {
 
@@ -50,7 +51,9 @@ export class Simctl implements ISimctl {
 
 	public async getAppContainer(deviceId: string, appIdentifier: string): Promise<string> {
 		try {
-			return await this.spawnAsync("get_app_container", [deviceId, appIdentifier]);
+			const appContainerPath = await this.spawnAsync("get_app_container", [deviceId, appIdentifier]);
+			// In case application is not installed on simulator, get_app_container returns some random location. After you installation, the application goes in a different location.
+			return fs.existsSync(appContainerPath) ? appContainerPath : null;
 		} catch (e) {
 			if (e.message.indexOf("No such file or directory") > -1) {
 				return null;