Fix TestFdLeak on Linux.

Summary:
LLGS leaks pipes (when launched by lldb), sockets (when launched by platform),
and/or log file to the inferior. This should prevent all possible leaks.

Reviewers: vharron, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9211

llvm-svn: 235615