[fix] update fails if no remote found

- The bench update used to fail if there was no remote found for the app.
Fixed by adding check if remote exists. If it doesn't the app is added
to excluded_apps.txt and not considered for an update
- [minor] optimized get_excluded_apps list by calling it only once, as
opposed to getting it for every app

bench/app.py

@@ -222,14 +222,19 @@ Here are your choices:
 	wait for them to be merged in the core.'''.format(app))
 					sys.exit(1)
 
+	excluded_apps = get_excluded_apps()
 	for app in get_apps(bench_path=bench_path):
-		excluded_apps = get_excluded_apps()
 		if app in excluded_apps:
 			print("Skipping pull for app {}".format(app))
 			continue
 		app_dir = get_repo_dir(app, bench_path=bench_path)
 		if os.path.exists(os.path.join(app_dir, '.git')):
 			remote = get_remote(app)
+			if not remote:
+				# remote is False, i.e. remote doesn't exist, add the app to excluded_apps.txt
+				add_to_excluded_apps_txt(app, bench_path=bench_path)
+				print("Skipping pull for app {}, since remote doesn't exist, and adding it to excluded apps".format(app))
+				continue
 			logger.info('pulling {0}'.format(app))
 			if reset:
 				exec_cmd("git fetch --all", cwd=app_dir)
@@ -276,12 +281,13 @@ def get_remote(app, bench_path='.'):
 									   stderr=subprocess.STDOUT)
 	contents = contents.decode('utf-8')
 	if re.findall('upstream[\s]+', contents):
-		remote = 'upstream'
+		return 'upstream'
+	elif not contents:
+		# if contents is an empty string => remote doesn't exist
+		return False
 	else:
 		# get the first remote
-		remote = contents.splitlines()[0].split()[0]
-
-	return remote
+		return contents.splitlines()[0].split()[0]
 
 def use_rq(bench_path):
 	bench_path = os.path.abspath(bench_path)