change test/addons/ to ignore empty folders

[Fishrock123]

• Version: all with /addons/ tests
• Platform: at least macOS and Linux
• Subsystem: test

When changing branches sometimes git seems to leave empty folders behind which in the case of the test/addons/ directory causes at least gyp to explode with an error similar to:

Building addon /Users/Jeremiah/Documents/node/test/addons/async-hooks-id/
gyp: binding.gyp not found (cwd: /Users/Jeremiah/Documents/node/test/addons/async-hooks-id) while trying to load binding.gyp
Makefile:192: recipe for target 'test/addons/.buildstamp' failed
make[1]: *** [test/addons/.buildstamp] Error 1
make[1]: Leaving directory '/Users/Jeremiah/Documents/node'
Makefile:133: recipe for target 'test' failed
make: *** [test] Error 2

[addaleax]

@Fishrock123 This is not a Python thing, build was appropriate (the error pops up while building the addons from our Makefile, not in the test runner) :)

[refack]

If anyone want to tackle this but hits the GYP wall, feel free to ping me.

[vnktram]

Working on it.

[vnktram]

Unable to replicate even after switching between branches.