tests: Fix evpn tests to ensure mac addresses will show up

tests: Fix evpn tests to ensure mac addresses will show up

Locally, the bgp_evpn_vxlan_svd_topo1 and bgp_evpn_vxlan_topo1
tests are failing for me.  Upon inspection the test is looking
for the mac addresses of the interfaces participating in the
evpn bridging on the hosts.  For some reason on my machine
these mac addresses are not in the l2 tables at all on
PE1 or PE2.  Adding quick pings solves the problems.

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