fastboot driver: RunAndReadBuffer don't allocate too much mem

Instead of allocating the buffer for the whole
upload (which can be arbitrary number of bytes as
the device determines), read 1 MiB at a time.

Test: pass
Bug: 173654501
Change-Id: Ib601b0341b10b7dccbb429cd21aad86a2d3bfda8
3 files changed