[show_sflow_test.py]: Fix show sflow display and Sflow Tests.

[praveen-li]

Changes:
-- Display ipv4 address with left adjust of 25 width and with space before UDP.
-- IPv6 address will be displayed as is.
-- Add test data to appl_db.json and config_db.json
-- add test file show_sflow_test.py

Signed-off-by: Praveen Chaudhary pchaudhary@linkedin.com

- What I did
Changes:
-- Display ipv4 address with left adjust of 25 width and with space before UDP.
-- IPv6 address will be displayed as is.
-- Add test data to appl_db.json and config_db.json
-- add test file show_sflow_test.py

- How I did it
Display ipv4 address with left adjust of 25 width and with space before UDP.

- How to verify it
-- Add test data to appl_db.json and config_db.json
-- add test file show_sflow_test.py

Built with above test:

pchaudha@server05:/home/pchaudha/srcCode/azure_myforks/sonic-buildimage$ date
Fri Aug 14 14:01:58 PDT 2020
pchaudha@server05:/home/pchaudha/srcCode/azure_myforks/sonic-buildimage$ ls -l target/python-debs/python-sonic-utilities_1.2-1_all.deb
-rw-r--r-- 1 pchaudha pchaudha 168448 Aug 14 14:01 target/python-debs/python-sonic-utilities_1.2-1_all.deb

- Previous command output (if the output of a command-line utility has changed)
Before Fix:

show sflow
 
sFlow Global Information:
  sFlow Admin State:          up
  sFlow Polling Interval:     0
  sFlow AgentID:              eth0
 
  2 Collectors configured:
    Name: prod                IP addr: 10.252.194.107UDP port: 6343
    Name: ser5                IP addr: 172.21.47.15UDP port: 6343

- New command output (if the output of a command-line utility has changed)
After Fix:

admin@lnos-x1-a-asw04:~$ show sflow

sFlow Global Information:
  sFlow Admin State:          up
  sFlow Polling Interval:     0
  sFlow AgentID:              eth0

  2 Collectors configured:
    Name: prod                IP addr: 10.252.194.107  UDP port: 6343
    Name: ser5                IP addr: 172.21.47.15    UDP port: 6343


admin@lnos-x1-a-asw04:~$ show sflow

sFlow Global Information:
  sFlow Admin State:          up
  sFlow Polling Interval:     0
  sFlow AgentID:              eth0

  2 Collectors configured:
    Name: prod                IP addr: fe80::6e41:6aff:fe1e:cd8e UDP port: 6343
    Name: ser5                IP addr: 172.21.47.15    UDP port: 6343

[praveen-li]

retest this please