[bgpmon]Add new test case test_bgpmon#2521

Merged

bingwang-ms merged 5 commits intosonic-net:masterfrom

bingwang-ms:add_bgpmon_test

Nov 18, 2020

Commits on Nov 12, 2020

Commits on Nov 13, 2020

Update after review.
bingwang-ms
committed

Commits on Nov 16, 2020

Update veos_vtb for addressing ptf login issue
bingwang-ms
committed

Commits on Nov 17, 2020

Add a new case for verifying bgpmon when resolve-via-default is disabled
bingwang-ms
committed