[TS/TSA/B/C]: Update traffic-shift scripts with bgp neighbor check enhancement

[Stephenxf]

Why I did it

The test case test_TSA_B_C_with_no_neighbors from bgp/test_traffic_shift.py may fail because of the way ebgp neighbors are counted in sonic-buildimage/dockers/docker-fpm-frr/TSA in source code or /usr/bin/TSA in bgp container (the same applies to TSB and TSC as well). Our (LinkedIn) configuration profile is a bit different, but the issue should be common.

If there is no eBGP neighbor, TSA/TSB/TSC are supposed to return "System Mode: No external neighbors". However, this "no eBGP" check is done by looking at the number of route-maps from running-config.

In buildimage/dockers/docker-fpm-frr/TSA:

find_num_routemap
routemap_count=$?
check_not_installed
not_installed=$?

if [[ $routemap_count -eq 0 ]];
then
  echo "System Mode: No external neighbors"

In buildimage/dockers/docker-fpm-frr/TS:

function find_num_routemap()
{
  c=0
  config=$(vtysh -c "show run")
  for route_map_name in $(echo "$config" | sed -ne 's/  neighbor \S* route-map \(\S*\) out/\1/p' | egrep 'V4|V6' | uniq);
  do
    is_internal_route_map $route_map_name && continue
    c=$((c+1))
  done
  return $c
}

The idea is to find out the number of ebgp neighbors by checking if any ebgp-specific outbound route-maps are being used by any neighbors. However, this can be problematic and lead to incorrect result, in twofold:

• The numebr of "neighbor ... route-map ... out" doesn't always equal the number of neighbors. For example, if peer-groups are configured and a set of bgp neighbors are inheriting outbound route-maps via peer-groups, the find_num_routemap won't return the correct number of ebgp neighbors. Similar problem would happen with dynamic neighbors.
• As demonstrated by the test case test_TSA_B_C_with_no_neighbors, when all the neighbors are gone (e.g., deleted via sonic-cfggen), the peer-groups can still be there in running-config. As a result, TSA/TSB/TSC won't show the expected result, i.e., "System Mode: No external neighbors".

How I did it

We can get the eBGP neighbor count by checking "show bgp summary". This proposal introduces a function find_num_ebgp_neighbors to parse "show bgp summary json" output and return the number of eBGP neighbors (remote-ASN different from local-ASN).

How to verify it

1. Run Pytest case test_TSA_B_C_with_no_neighbors from bgp/test_traffic_shift.py.
2. Unit test of TSA/TSB/TSC with:

• no BGP neighbor
• no eBGP neighbor but iBGP neighbors
• both eBGP and iBGP neighbors

Which release branch to backport (provide reason below if selected)

Description for the changelog

Update traffic-shift scripts with bgp neighbor check enhancement.

A picture of a cute animal (not mandatory but encouraged)

[ghost]

All CLA requirements met.

[lguohan]

@abdosi , can you check this pr?