fastboot fails to do anything because of -i option

!857 (merged) introduced flash_fastboot_vendor_id, which adds -i option to fastboot's args. The problem is that -i option got removed in https://android.googlesource.com/platform/system/core/+/f3192bd05231eb6d1c9307885c5400494e38527f%5E%21/ so pmbootstrap can't flash anything on devices that use fastboot. Error message is:

(022844) [13:06:10] (native) % fastboot -i flash userdata /home/pmos/rootfs/lg-hammerhead.img
fastboot: unrecognized option: i

There are two solutions:

1. revert 6fb5b28e (might break flashing on amazon-thor)
2. package older version of android-tools and use it if flash_fastboot_vendor_id is set (harder, but doesn't break anything)