Fix Ftp Download failed with muti IP Login

1 Lock when GetFtpClient to void login mutitimes
2 use tcp4 when ipv6 is not active
3 fix failed ftp server return muti-line when Retr

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/14391fa62c59459b8ebf4bbe18a5483f/

Change-Id: Ic8187a7736b990173298fb87e242e332817c0a87
Merge "Fix Ftp Download failed with muti IP Login"