Android P版本烧录GSI

Android P之后烧录GSI相对于android O有了一些变化，Android O 环境配置和GSI烧录请参考android 8.1 VTS环境配置

Mtk平台：

MTK User load boot up to home screen
Please enable OEM unlocking in settings
Press volume up key + power key into fastboot mode
Connect phone to PC and then type following commands
adb reboot bootloader
fastboot flashing unlock
fastboot erase system  ------Android P新增
fastboot flash system system.img (system.img is GSI)
fastboot --disable-verification flash vbmeta vbmeta.img  ---------- Android P新增
(vbmeta.img is MTK's vbmeta.img. Please get it from MTK load.)
fastboot reboot

如果不做fastboot erase system 和 fastboot --disable-verification flash vbmeta vbmeta.img会导致烧录GSI之后无法开机，无限重启