fs: make rmdir() emfileWait handle ENFILE

[bnoordhuis]

1. EMFILE: current process is out of file descriptors
2. ENFILE: system is out of file descriptors

The fs.rmdir() logic in lib/internal/fs/rimraf.js currently handles the former but not the latter:

node/lib/internal/fs/rimraf.js

Lines 43 to 44 in ed40123

	if (err.code === 'EMFILE' && timeout < options.emfileWait)
	return setTimeout(_rimraf, timeout++, path, options, CB);

Both are (hopefully) transient errors though and should be handled identically.

Since ENFILE is difficult to test for, I think it's okay to omit a regression test.

[thangktran]

I would like to work on this issue

[bnoordhuis]

@thangktran Go for it :)