core: fastboot: Fix data not being wiped on do_update

 * With platform-tools-34.0.4 if you try to wipe data
   as apart of the fastboot update command it will not
   work, will just reboot to userspace without running
   the wipe task.

Test: fastboot -w update image.zip, observe that data
      gets wiped. Also verified 'fastboot update image.zip'
      does *not* wipe data.
Change-Id: I57a2c64029fd4f78968324bdf60251e1e962b3fd