New framework for lldb client-server communication tests.

Summary:
This is a new C++ test framework based on Google Test, and one working
example test.
The intention is to replace the existing tests in
packages/Python/lldbsuite/test/tools/lldb-server/ with this suite
and use this framework for all new client server tests.

Reviewers: labath, beanz

Reviewed By: labath, beanz

Subscribers: beanz, emaste, zturner, tberghammer, takuto.ikuta, krytarowski, mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D32930
Patch by Jason Majors <jmajors@google.com>

llvm-svn: 304793