ovn-nbctl: Update logical router port commands.

ovn-nbctl: Update logical router port commands.

A few minor changes related to logical router port commands:

    - Use "lrp" instead of "lrport" to be more consistent with later
      changes.
    - Use commands where possible in ovn unit tests.
    - Move documentation to group router commands together.
    - Adds mac/network/peer to lrp-add command.  The existing command
      doesn't require creating a mac or network address, which shouldn't
      be possible.
    - Drops lrport-[get|set]-mac-addresses commands in favor of
      initializing them in lrp-add command.
    - Update references from "lrport" to "lrp" (code) or "port" (user).

Signed-off-by: Justin Pettit <jpettit@ovn.org>
Acked-by: Ryan Moats <rmoats@us.ibm.com>
Acked-by: Ben Pfaff <blp@ovn.org>