Updated configure.ac to 0.18.0.
Added LLDB convenience scripts.

This patch adds lldb-mesos-tests, lldb-mesos-local, lldb-mesos-master
and lldb-mesos-slave in similar style as gdb-mesos-* as GDB seems to
have been out phased on OS X Mavericks.

Review: https://reviews.apache.org/r/17445