Kill any python test script that takes more than 5 minutes

There is at least one test that hangs on the Linux debian buildbot.

When that test hangs, the buildbot kills dosep which loses all test
results.  This change kills just the hung test and should let us see
which test is hanging.  This is useful for that test and any others
in the future which start hanging.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@223423 91177308-0d34-0410-b5e6-96231b3b80d8