win: Use the _winreg module for registry access

win: Use the _winreg module for registry access

This commit changes the Visual Studio installation path detection code to use
_winreg to find the installation path in the registry.  The previous method of
using reg.exe is preserved as a fallback for when '_winreg' cannot be imported
(for example in cygwin).

Also, remove the '_RegistryKeyExists' function since it is not used anywhere.

BUG=
R=scottmg@chromium.org

Committed: https://code.google.com/p/gyp/source/detail?r=2002

[Shezan Baig (Bloomberg), 2014-11-13 17:58:42]

sbaig1@bloomberg.net changed reviewers:
+ scottmg@chromium.org

[scottmg, 2014-11-13 18:05:35]

lgtm

https://codereview.chromium.org/724863002/diff/1/pylib/gyp/MSVSVersion.py
File pylib/gyp/MSVSVersion.py (right):

https://codereview.chromium.org/724863002/diff/1/pylib/gyp/MSVSVersion.py#new...
pylib/gyp/MSVSVersion.py:180: root,subkey = key.split('\\', 1)
nit; space after ,

https://codereview.chromium.org/724863002/diff/1/pylib/gyp/MSVSVersion.py#new...
pylib/gyp/MSVSVersion.py:181: assert('HKLM' == root)  # Only need HKLM for now
nits;
- no ()
- root == 'HKLM', rather than yoda-style
- '.' at end of comment.

https://codereview.chromium.org/724863002/diff/1/pylib/gyp/MSVSVersion.py#new...
pylib/gyp/MSVSVersion.py:189: """Use _winreg or reg.exe to obtain the value of a
registry key.
add a comment explaining why we need to try both ways

[Shezan Baig (Bloomberg), 2014-11-13 18:46:50]

Thanks for the quick review!  I've uploaded a new patch with the changes

[scottmg, 2014-11-13 18:51:33]

lgtm

[Shezan Baig (Bloomberg), 2014-11-13 19:46:33]

Committed patchset #2 (id:20001) manually as 2002 (presubmit successful).