xcode-ninja doesn't respect --generator-output for generated Xcode workspace

What steps will reproduce the problem?
1. gyp -f xcode-ninja --generator-output output project.gyp

What is the expected output? 
./output/project.ninja.xcodeproj 
./output/sources_for_indexing.xcodeproj
./output/project.ninja.xcworkspace

What do you see instead?
./output/project.ninja.xcodeproj 
./output/sources_for_indexing.xcodeproj
./project.ninja.xcworkspace

What version of the product are you using? On what operating system?
master / OS X 10.9.4

Please provide any additional information below.
The bug is that project.ninja.xcworkspace should also go into 'output'.

I have attached two patches: 

The first one fixes the issue. From reading the code, it appears as if the 
xcode-ninja generator is not yet tested, so it also adds the new class 
TestGypXcodeNinja to be able to test the change. The existing test 
generator-output/gyptest-top-all.py already catches the bug when run using 
TestGypXcodeNinja, so I didn't add a new test.

The second patch adapts the other generator-output tests to the xcode-ninja 
generator. It is not necessary for the bugfix, but may be a start towards 
better test coverage of the xcode-ninja generator.

I would kindly ask you to review my patches and commit as you see fit.

Original issue reported on code.google.com by ab1...@gmail.com on 21 Jul 2014 at 8:50

Attachments:

iceman5555 / gyp

xcode-ninja doesn't respect --generator-output for generated Xcode workspace #442