[lit] Fix handling of per test timeout when the installed psutil version
is < ``2.0``.

Older versions of psutil (e.g. ``1.2.1`` which is the version shipped with
Ubuntu 14.04) use a different API for retrieving the child processes.
To handle this try the new API first and if that fails try the old API.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257616 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed