Refactor Policy Tests

[wenovus]

• Expanded generic policy_test topology to accommodate different tests.
• Factored out route propagation checking logic, which now can also check a new NOT_PREFERRED state.
• lemming device creation is done more automatically, with each listening only on its own address instead of on all addresses.
• Parallelize session establishment.
• community_set_test.go will be deleted in the next PR so can skip reviewing that.
• Install filtering policies on the import side due to GoBGP not supporting route withdrawals when soft-resetting on the export side.

[wenovus]

Converting to a draft for now to see if the test time can be reduced, and potentially remove test from running on GitHub.

[wenovus]

I noticed the "update is stale" error when running the BGP integration tests locally under high CPU load. I haven't seen it locally otherwise.

[DanG100]

//integration_tests/twodut_oneotg_tests/bgp_redistribution:bgp_redistribution_test is failing locally on my machine can you take a look

[wenovus]

The "update is stale" error is appearing now on GCB as well. I will investigate this later. It's clear it's not just happening on GitHub.