Fix "git cl upload --use-oauth2" not working on Windows when HOME is not set.

Fix "git cl upload --use-oauth2" not working on Windows when HOME is not set.

depot_tools' git wrapper for some reason overrides %HOME% to point to
depot_tools directory, and thus scripts running as git subprocesses (git_cl.py)
use not the same HOME as scripts that run outside of git process tree
(depot-tools-auth.py). Instead always use USERPROFILE in auth.py to consistently
pick same directory.

This issue happens only when HOME is not set globally. It can explain why it
wasn't seen earlier.

R=iannucci@chromium.org
BUG=356813
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=294911

[Vadim Sh., 2015-04-21 01:17:30]

PTAL

I had three choices:
1) Do it like in this CL.
2) At same hack with HOME to depot-tools-auth.bat.
3) Unhack HOME in git.

(3) is too difficult for me, and who knows what will it break.
I choose (1). Perhaps I should do (2) instead? I'm bad with batch scripts... the
line that sets HOME looks like a set of symbols to me.

[iannucci, 2015-04-21 01:22:51]

Super gross.... lgtm . meh.

should really get rid of the hack in the git commands.

[Vadim Sh., 2015-04-21 01:40:38]

The CQ bit was checked by vadimsh@chromium.org

[commit-bot: I haz the power, 2015-04-21 01:40:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1082833004/1

[commit-bot: I haz the power, 2015-04-21 01:44:16]

Committed patchset #1 (id:1) as
http://src.chromium.org/viewvc/chrome?view=rev&revision=294911