tests: Reduce some pim test timings to more manageable levels

tests: Reduce some pim test timings to more manageable levels

a) Remove the retry mechanism to continue looking for 75%
of the time for pim code.

   This alone saves a bunch of time in tests that use lib/pim.py
   Effectively all the times given for retry are already long
   enough.  Additionally some tests are gathering data with
   the expectation that they will not find data so the entire
   time is being taken up in retry's.  Extending the retry
   mechanism makes this even worse.  This is especially bad
   for pim in that keep alive timers are counting down and
   state can be removed due to excessive time waiting.

b) Reduce verify verify_multicast_traffic from 40 seconds
to 20 seconds to gather traffic data.

   A bunch of tests are doing this:
   a) gather pre test start traffic data( taking about 70
   seconds to run, because a bunch of time it was looking
   for data that does not exist yet)
   b) run a change to introduce a different traffic flow
   c) gather post test traffic data ( taking about 70
   seconds to run )

   Why does this matter?  Tests were iterating through
   all the different routers looking for traffic flow
   as well as different mroute state.  This is against
   the keepalive timer of 210 seconds.  It does not take
   long before the stream can be removed and the test is
   still looking for data that is no longer there due
   to state timeout.

   The multicast_pim_sm_topo3/test_multicast_pim_sm_topo3.py
   test reduced run time from 398 seconds to 297 seconds.
   Greatly reducing keepalive timeout problems.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>
(cherry picked from commit de3d6b4db41eb3c3d3c88c0009ba647271d2f2b1)