[Fuchsia] Use QEMU and QEMU host tools downloaded from CIPD.

QEMU will soon be removed from the Fuchsia SDK tarball.
This CL migrates our scripts to source QEMU from CIPD instead.

Change-Id: I2347a5be598a1eecd2d7c9e6c431b55c3eab1189
Reviewed-on: https://chromium-review.googlesource.com/1178975
Commit-Queue: Kevin Marshall <[email protected]>
Reviewed-by: Sergey Ulanov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#584238}
6 files changed