On Python 3, Mach doesn't set executable permission when extracting zips, breaking `bootstrap-android`

[zhuowei]

When running python3 ./mach bootstrap-android --build using Python 3, I get this error:

zhuowei@dora:~/servo-work/servo$ python3 ./mach bootstrap-android --build
Downloading https://dl.google.com/android/repository/android-ndk-r15c-linux-x86_64.zip ...
Downloading android-ndk-r15c-linux-x86_64.zip: 100.0%
Extracting android-ndk-r15c-linux-x86_64.zip
Downloading https://dl.google.com/android/repository/sdk-tools-linux-4333796.zip ...
Downloading sdk-tools-linux-4333796.zip:  99.8%
Extracting sdk-tools-linux-4333796.zip
Error running mach:

    ['bootstrap-android', '--build']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.
You can invoke |./mach busted| to check if this issue is already on file. If it
isn't, please use |./mach busted file| to report it. If |./mach busted| is
misbehaving, you can also inspect the dependencies of bug 1543241.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

PermissionError: [Errno 13] Permission denied: '/home/zhuowei/servo-work/servo/android-toolchains/sdk/tools/bin/sdkmanager'

  File "/home/zhuowei/servo-work/servo/python/servo/bootstrap_commands.py", line 185, in bootstrap_android
    subprocess.check_call(sdkmanager)
  File "/usr/lib/python3.7/subprocess.py", line 358, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python3.7/subprocess.py", line 339, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.7/subprocess.py", line 800, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.7/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)

It looks like

servo/python/servo/util.py

Line 174 in 7596a0f

# https://stackoverflow.com/questions/39296101/python-zipfile-removes-execute-permissions-from-binaries

is supposed to set the executable bit when extracting zips, but the linked Stack Overflow issue states that the current workaround broke on Python 3.6 and above.

[garasubo]

As the second and third answer in that Stack Overflow issue, this is because this library uses different method in it in Python 3.6 and later.