run_host_test: some cleanups
run_host_test: some cleanups

Chris suggested some good cleanups in CL:3105736, but this was just a
firmware-branch cherry pick of a CL from >1yr ago.

Making these changes on ToT instead.  Summary of the changes:

- Remove obsolete __future__ import since we only run on Python 3 now.
- Use explicit 0, 1, 2, 3 exit codes for success, failure, timeout,
  and unexpected termination (respectively).  This lets us drop a
  property.
- Read from the process in unicode mode, since we just end up decoding
  later anyway.
- verbose argument changed from counter to boolean since there's no
  additional behavior created by passing multiple times.

BUG=none
BRANCH=none
TEST=make buildall -j32

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Ibc9de7d45f5ac1242429481c6bc5f303cdef6b06
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3107925
Commit-Queue: Chris McDonald <4ca9f429749ea29f0277a76979656ec13beb5513@chromium.org>
Reviewed-by: Chris McDonald <4ca9f429749ea29f0277a76979656ec13beb5513@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec