We were not decoding the stdout bytes before printing them when git
commands returned an error status. This CL fixes that.

Before:
Command "git cherry-pick FETCH_HEAD" failed.
b'Auto-merging chrome/browser/ui/web_applications/app_browser_controller.cc\nAuto-merging chrome/browser/ui/views/frame/opaque_browser_frame_view_browsertest.cc\nCONFLICT (content): Merge conflict in chrome/browser/ui/views/frame/opaque_browser_frame_view_browsertest.cc\nAuto-merging chrome/browser/ui/views/frame/browser_non_client_frame_view.cc\nAuto-merging chrome/browser/ui/views/frame/browser_frame.h\nAuto-merging chrome/browser/ui/views/frame/browser_frame.cc\n'

After:
Command "git cherry-pick FETCH_HEAD" failed.
Auto-merging chrome/browser/ui/web_applications/app_browser_controller.cc
Auto-merging chrome/browser/ui/views/frame/opaque_browser_frame_view_browsertest.cc
CONFLICT (content): Merge conflict in chrome/browser/ui/views/frame/opaque_browser_frame_view_browsertest.cc
Auto-merging chrome/browser/ui/views/frame/browser_non_client_frame_view.cc
Auto-merging chrome/browser/ui/views/frame/browser_frame.h
Auto-merging chrome/browser/ui/views/frame/browser_frame.cc
Change-Id: I162e666ca9f3a70259e6178d2e6d3b72f15b1f7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2310016
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>