Mark the other test of TestFdLeak also as xfail to keep the bot green.

Summary:
r235916 marked only one of the tests as xfail, but the other also has
been failing intermitantly on the buildbot.

Reviewers: chaoren

Reviewed By: chaoren

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9452

llvm-svn: 236366