使用repo方式下载android代码

1. 为所有的git工程建立本地分支

/*repo下载后默认没有本地分支的，新建本地master分支*/

repo start master --all

2. repo start说明：

localhost FactoryTest # repo help start

Summary
-------
Start a new branch for development

Usage: repo start <newbranchname> [--all | <project>...]

Options:
  -h, --help  show this help message and exit
  --all       begin branch in all projects

Description
-----------
'repo start' begins a new branch of development, starting from the
revision specified in the manifest.