tests: Add another router to the basic pim tests

tests: Add another router to the basic pim tests

Add an additional router to the basic pim tests.
1) This test will add a link between r1 and a new rp
2) This test will ensure that r1 and rp have the expected
who is the rp.
3) This test will ensure that the rp has received the upstream
data for the multicast stream that is started.

Ostensibly commit
68a02e06e5f103048d947262c08c569056f74d1c is the first bad commit
commit 68a02e06e5f103048d947262c08c569056f74d1c
Author: Mark Stapp <mjs@voltanet.io>
Date:   Wed Nov 13 16:06:06 2019 -0500
    *: revise zapi nexthop encoding
    Use a per-nexthop flag to indicate the presence of labels; add
    some utility zapi encode/decode apis for nexthops; use the zapi
    apis more consistently.
    Signed-off-by: Mark Stapp <mjs@voltanet.io>
Sparked this commit in that it broke nexthop reporting to upper
level protocols.  Ensure that this expectation stays working
in the future.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>