Fixes path issue in Windows exe launchers

Using spaces in Windows is common. This patch fixes an issue in the exe launch
wrappers generated in the "Scripts" directory where unnecessary quoting causes
the following error.

Fatal error in launcher: Unable to create process using '""C:\Program Files (x86)\Cloudbase    Solutions\OpenStack\Nova\Python27\python.exe"" "C:\Program Files (x86)\Cloudbase Solutions\OpenStack\Nova\Python27\Scripts\nova.exe" '

Closes issue: pypa#1997

pip/_vendor/distlib/scripts.py

@@ -92,7 +92,6 @@ def _get_alternate_executable(self, executable, options):
         return executable
 
     def _get_shebang(self, encoding, post_interp=b'', options=None):
-        enquote = True
         if self.executable:
             executable = self.executable
             enquote = False     # assume this will be taken care of
@@ -109,10 +108,6 @@ def _get_shebang(self, encoding, post_interp=b'', options=None):
         if options:
             executable = self._get_alternate_executable(executable, options)
 
-        # If the user didn't specify an executable, it may be necessary to
-        # cater for executable paths with spaces (not uncommon on Windows)
-        if enquote and ' ' in executable:
-            executable = '"%s"' % executable
         executable = fsencode(executable)
         shebang = b'#!' + executable + post_interp + b'\n'
         # Python parser starts to read a script using UTF-8 until