Fixed python API event test cases.

Issues were:
1 - It isn't good to have more than one listener for the process events, just supply a listener at launch instead of making a one then have the process broadcaster add a new listener
2 - run in async mode



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@220113 91177308-0d34-0410-b5e6-96231b3b80d8