Close terminal after LaunchInTerminalTestCase test

Summary:
The test_launch_in_terminal test leaves a running terminal.
This patch adds "exit" after debugging with eLaunchFlagLaunchInTTY flag.

Reviewers: jingham, zturner, clayborg

Reviewed By: clayborg

Subscribers: emaste, vharron, lldb-commits, clayborg, jingham, zturner

Differential Revision: http://reviews.llvm.org/D7468

llvm-svn: 228801