Fix pip installs on Windows.

[arsharma1]

The setup script had an undefined variable when installing on Windows. It shouldn't get into that code in the first place.

Fixes #881

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This change is 

[orgroman-dev]

This fix should resolve the issue (I'll test it later on).
Thing is, is it still required to drop support for protocol buffer on windows?

Seems like there was an attempt here:
#723

[arsharma1]

@Hfusi0n please try with this commit. I've ported the relevant bits from the other pull request.

[orgroman-dev]

@Hfusi0n please try with this commit. I've ported the relevant bits from the other pull request.

I should have tested this pull request before referencing to it, sorry...
This will cause an exception if the find executable fails (just tested it on my laptop):

I think first commit should be merged making sure installation doesn't throw exceptions I tested your first commit and it seems to work as excepted.

Second commit might need to be tested more - see below error log.

EDIT

It's possible (and tested on my laptop) to support protoc on windows if using the compiled version by Google:

protocolbuffers/protobuf#5205

I've added the protoc executable to my PATH and changed the setup file for the prefix to include protoc include directory and everything worked fine.

Since protoc is a third party to this project I'm not really sure what to do here.

running build_proto
Traceback (most recent call last):
File "setup.py", line 59, in initialize_options
'pkg-config --variable prefix protobuf'.split()).strip().decode('utf-8')
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\subprocess.py", line 395, in check_output
**kwargs).stdout
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\subprocess.py", line 472, in run
with Popen(*popenargs, **kwargs) as process:
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\subprocess.py", line 775, in init
restore_signals, start_new_session)
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\subprocess.py", line 1178, in _execute_child
startupinfo)
FileNotFoundError: [WinError 2] The system cannot find the file specified

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "setup.py", line 220, in
'pytest-cov>=2.2.1',
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\site-packages\setuptools_init_.py", line 145, in setup
return distutils.core.setup(**attrs)
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\distutils\core.py", line 148, in setup
dist.run_commands()
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\distutils\dist.py", line 966, in run_commands
self.run_command(cmd)
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\distutils\dist.py", line 983, in run_command
cmd_obj = self.get_command_obj(command)
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\distutils\dist.py", line 858, in get_command_obj
cmd_obj = self.command_obj[command] = klass(self)
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\distutils\cmd.py", line 62, in init
self.initialize_options()
File "setup.py", line 71, in initialize_options
os.path.dirname(os.path.dirname(os.path.dirname(self.protoc))),
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\ntpath.py", line 221, in dirname
return split(p)[0]
File "C:\ProgramData\Anaconda3\envs\DeviceQualityLibrary\lib\ntpath.py", line 183, in split
p = os.fspath(p)
TypeError: expected str, bytes or os.PathLike object, not NoneType

[cclauss]

git conflicts