gtest runner: now always does a clean step after running.

* Checks for any 'clean' arg, setting clean-only mode.
* If clean-only mode, skip the make.
* Adds the equivalent of os.devnull in a way that supports the file-like 'write' operation.
* Uses a null sysout/syserr for the clean step so we don't see noise from cleaning.
* Now always runs the clean step after a real test run so we don't have cruft left over after a test run.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218871 91177308-0d34-0410-b5e6-96231b3b80d8
thread state coordinator: requesting resume now signals error appropriately.

Added tests to verify that the coordinator signals an error if
the given thread to resume is unknown, and if the thread is through to
be running already.

Modified resume handling code to match tests.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218872 91177308-0d34-0410-b5e6-96231b3b80d8
Fix up stale comments from last change.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@218873 91177308-0d34-0410-b5e6-96231b3b80d8