[201911] Updated BBR to use peer group name as prefix.

[abdosi]

What/Why I did:

Same change as in master (PR #6515) for 201911.
In 201911 BBR is configured for each peer instead of peer-group.

How I verify:

• Manually Verified BBR is enabled/disabled correctly for the peer in the peer-group.

neighbor 10.0.0.33 peer-group TIER0_V4_DEPLOYMENT_ID_0
neighbor 10.0.0.63 peer-group TIER0_V4_DEPLOYMENT_ID_2
neighbor 10.0.0.33 allowas-in 1
neighbor 10.0.0.63 allowas-in 1
neighbor fc00::7a peer-group TIER0_V6_DEPLOYMENT_ID_0
neighbor fc00::7e peer-group TIER0_V6_DEPLOYMENT_ID_2
neighbor fc00::7a allowas-in 1
neighbor fc00::7e allowas-in 1

• Added Unit test

adosi@68cd7f721b7f:/sonic/src/sonic-bgpcfgd$ pytest tests/test_bbr.py
============================================================================================== test session starts ==============================================================================================
platform linux2 -- Python 2.7.13, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
rootdir: /sonic/src/sonic-bgpcfgd, inifile: pytest.ini
plugins: cov-2.4.0
collected 28 items

tests/test_bbr.py ............................

---------- coverage: platform linux2, python 2.7.13-final-0 ----------
Name                             Stmts   Miss  Cover
----------------------------------------------------
bgpcfgd/__init__.py                  0      0   100%
bgpcfgd/__main__.py                  3      3     0%
bgpcfgd/config.py                   69     69     0%
bgpcfgd/directory.py                63     34    46%
bgpcfgd/frr.py                      49     49     0%
bgpcfgd/log.py                      15      5    67%
bgpcfgd/main.py                     53     53     0%
bgpcfgd/manager.py                  41     23    44%
bgpcfgd/managers_allow_list.py     425    425     0%
bgpcfgd/managers_bbr.py             98      0   100%
bgpcfgd/managers_bgp.py            192    192     0%
bgpcfgd/managers_db.py               9      9     0%
bgpcfgd/managers_intf.py            33     33     0%
bgpcfgd/managers_setsrc.py          44     44     0%
bgpcfgd/runner.py                   44     44     0%
bgpcfgd/template.py                 64     42    34%
bgpcfgd/utils.py                    19     19     0%
bgpcfgd/vars.py                      1      0   100%
----------------------------------------------------
TOTAL                             1222   1044    15%


=========================================================================================== 28 passed in 0.23 seconds ===========================================================================================

[lguohan]

do we need this for master branch?

[lguohan]

also, can you check how to add the unit test for this feature?

@lguohan Added unit test cases.

[abdosi]

do we need this for master branch?

@lguohan Yes will be creating separate PR for master

[lguohan]

let's merge the master image pr and then cherry-pick.

[abdosi]

cherry-pick from master PR. Closing this.