lrdp-v2: Add `--eval' option

Although the `--shell' option can currently be used for ad-hoc
debugging, it's not ideal for scripting since it prints out a bunch of
other stuff during initialization.  Add a dedicated `--eval' option that
executes arbitrary Python code without printing anything else.

Change-Id: I9e24e6d140dd49208b850b2a17ac2f599a35657b