Bug 23051 - Fix zombie processes after lldb-server tests

Summary:
This patch fixes the following bug: https://llvm.org/bugs/show_bug.cgi?id=23181
For some reason some lldb-server tests should be kicked using SIGHUP and SIGINT before termination, otherwise it will leave a zombie process.
I think the reason is that the lldb-server will terminate a slave process if it gets the SIGHUP/SIGINT and if so it should be fixed in lldb-server.

The solution is to terminate process like it does the pexpect (including the delayafterterminate interval).

Also this patch reverts the following commits:
* r234549 - Skip lldb-server tests according to bug 23181
* r234765 - Skip a few tests on OS X according to the bug 23181
* r234803 - Skip the TestGdbRemoteRegisterState.test_grp_register_save_restore_works_no_suffix_debugserver_dsym test on OS X according to the bug 23181

Test Plan:
```
$ ps | grep Z | grep a.out | wc -l
447
$ ./dosep.py --options "-v --executable $INSTALLDIR/bin/lldb"
[...]
$ ps | grep Z | grep a.out | wc -l
447
```

Reviewers: jasonmolenda, clayborg, tberghammer

Reviewed By: clayborg

Subscribers: lldb-commits, dawn, tberghammer, clayborg, jasonmolenda

Differential Revision: http://reviews.llvm.org/D9019

llvm-svn: 235008