Fix dosep.py on windows after r240946

Summary:
On windows, global python variables are not automatically passed to child processes. This commit
makes sure the default timeout value is available to child processes by passing it directly.
I pass the whole dotest_opts value to the children, so we can use the other members as well if we
need to do it in the future.

Reviewers: amccarth

Subscribers: lldb-commits-list

Differential Revision: http://reviews.llvm.org/D10895

llvm-svn: 241459