Add a test directory stop-hook to test the newly added "target stop-hook" command.

This uses pexpect module to spawn a 'lldb' program and uses pseudo-TTY to talk to
the child application.

The test cases test setting breakpoints, adding a stop-hook with line range, and
verifies that when the inferior stops, the stop-hook will fire off when it is
within range and will not fire off when it is out of range.

llvm-svn: 127519