Add support for CLI commands in lldb-mi

Summary:
This patch adds support for CLI command in lldb-mi. It's useful ability which also was implemented in gdb.

All tests pass on OS X.

Test Plan: ./dotest.py -v --executable $BUILDDIR/bin/lldb tools/lldb-mi/interpreter/

Reviewers: ted, clayborg, abidh

Reviewed By: clayborg, abidh

Subscribers: jingham, lldb-commits, ted, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D8483

llvm-svn: 233112