Reland "use python3 for goma related scripts"

This reverts commit 59140d43.

Reason for revert:
Make this works in git bash.

Original change's description:
> Revert "use python3 for goma related scripts"
>
> This reverts commit 138ec7c5.
>
> Reason for revert:
> This might have caused the following issue:
> https://bugs.chromium.org/p/chromium/issues/detail?id=1221233
>
> Original change's description:
> > use python3 for goma related scripts
> >
> > This uses python3 like autoninja{,.bat}.
> > https://source.chromium.org/chromium/chromium/tools/depot_tools/+/main:autoninja
> > https://source.chromium.org/chromium/chromium/tools/depot_tools/+/main:autoninja.bat
> >
> > Change-Id: I4daf1892024358c5b7d88b1e32b15c82cb4411d2
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2968069
> > Commit-Queue: Dirk Pranke <dpranke@google.com>
> > Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
> > Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
> > Reviewed-by: Dirk Pranke <dpranke@google.com>
>
> Change-Id: Ideb5004cf18c91c1404066622244a8527f5248f3
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2972023
> Auto-Submit: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Dirk Pranke <dpranke@google.com>
> Reviewed-by: Dirk Pranke <dpranke@google.com>

Bug: 1221233
Change-Id: I815a774faa2e4fbca0f262667ea89709a09e146b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2979560
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>

goma_auth

@@ -6,9 +6,15 @@
 
 # See revert instructions in cipd_manifest.txt
 
+# In git bash on Windows, invoke the batch file.
+if [ "$(expr "$(uname -s)" : "^MINGW64_NT")" == "10" ]; then
+    goma_auth.bat "$@"
+    exit
+fi
+
 MYPATH=$(dirname "${BASH_SOURCE[0]}")
 
 source "$MYPATH/cipd_bin_setup.sh"
 cipd_bin_setup &> /dev/null
 
-PYTHONDONTWRITEBYTECODE=1 exec python "$MYPATH/.cipd_bin/goma_auth.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python3 "$MYPATH/.cipd_bin/goma_auth.py" "$@"

goma_auth.bat

@@ -6,5 +6,5 @@
 :: See revert instructions in cipd_manifest.txt
 
 @call "%~dp0\cipd_bin_setup.bat" > nul 2>&1
-@call python.bat %~dp0\.cipd_bin\goma_auth.py %*
+@call %scriptdir%python-bin\python3.bat %~dp0\.cipd_bin\goma_auth.py %*
 exit /b

goma_ctl

@@ -6,9 +6,15 @@
 
 # See revert instructions in cipd_manifest.txt
 
+# In git bash on Windows, invoke the batch file.
+if [ "$(expr "$(uname -s)" : "^MINGW64_NT")" == "10" ]; then
+    goma_ctl.bat "$@"
+    exit
+fi
+
 MYPATH=$(dirname "${BASH_SOURCE[0]}")
 
 source "$MYPATH/cipd_bin_setup.sh"
 cipd_bin_setup &> /dev/null
 
-PYTHONDONTWRITEBYTECODE=1 exec python "$MYPATH/.cipd_bin/goma_ctl.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python3 "$MYPATH/.cipd_bin/goma_ctl.py" "$@"

goma_ctl.bat

@@ -6,5 +6,5 @@
 :: See revert instructions in cipd_manifest.txt
 
 @call "%~dp0\cipd_bin_setup.bat" > nul 2>&1
-@call vpython.bat %~dp0\.cipd_bin\goma_ctl.py %*
+@call %scriptdir%python-bin\python3.bat %~dp0\.cipd_bin\goma_ctl.py %*
 exit /b