Remove lldb streams from the Log class completely

Summary:
previously we switched to llvm streams for log output, this completes
the switch for the error streams.

I also clean up the includes and remove the unused argument from
DisableAllLogChannels().

This required adding a bit of boiler plate to convert the output in the
command interpreter, but that should go away when we switch command
results to use llvm streams as well.

Reviewers: zturner, eugene

Subscribers: lldb-commits, emaste

Differential Revision: https://reviews.llvm.org/D30894

llvm-svn: 297812