gsutil.py.bat: Skip updating depot_tools if DEPOT_TOOLS_UPDATE=0.
gsutil.py.bat: Skip updating depot_tools if DEPOT_TOOLS_UPDATE=0.

Bug: 1090603
Change-Id: I05ce5628320b36bf81fe7028d8c84427758395f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2229064
Reviewed-by: Arthur Wang <4dd6e087af8869f14b984774073ebecc342269bd@google.com>
Reviewed-by: Josip Sokcevic <4606aec58cba917397ff2e4738f995e4758694f8@google.com>
Commit-Queue: Edward Lesmes <d05609f027dc667cc37492b1dc1bdea5d60fa82a@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools