smoketest: T4387: Add test for load-balancing wan

[sever-sever]

Change Summary

Create 2 network namespaces that allow us to emulate 2 ISP
with different static addresses
Check routing table 201 for the first ISP and table 202 for the
second ISP. Each table must contain the default route
Check table mangle

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4387

Component(s) name

Proposed changes

How to test

vyos@r1:~$ /usr/libexec/vyos/tests/smoke/cli/test_load_balancning_wan.py
test_table_routes (__main__.TestLoadBalancingWan) ... ok

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Ran 1 test in 9.776s

OK

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly