ovn-nbctl: Update logical switch port commands.

ovn-nbctl: Update logical switch port commands.

A few minor changes related to logical switch port commands:

    - Use "lsp" instead of "lport" to be more consistent with later
      changes.
    - Use commands where possible in ovn unit tests.
    - Update references from "lport" to "lsp" (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>