Use shared pointers to hold the process in ProcessMonitor

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@185946 91177308-0d34-0410-b5e6-96231b3b80d8
Change TestRegisters.py attach case to attach to a.out and enable that test case

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@185947 91177308-0d34-0410-b5e6-96231b3b80d8