NativeProcessLinux: Merge operation and monitor threads
This commit moves the functionality of the operation thread into the new monitor thread. This is
required to avoid a kernel race between the two threads and I believe it actually makes the code
Test Plan: Ran the test suite a couple of times, no regressions.
Reviewers: ovyalov, tberghammer, vharron
Subscribers: tberghammer, lldb-commits
Differential Revision: http://reviews.llvm.org/D9080