fix leaking TCP connections which leads to consistent conformance test failures

[gauravkghildiyal]

What type of PR is this?

/kind bug
/kind test

What this PR does / why we need it:

The problem:

• At present, each HTTP request creates a new TCP connection within our tests.
• We make keep-alive HTTP requests which means that after the HTTP request completes, we don't close the TCP connection.
• While we are waiting for convergence, we continuously make HTTP requests which keep on leaking TCP connections.

# Example of active TCP connections to a Gateway with IP 42.54.109.216
❯ ss -tan | grep 42.54.109.216 | head -n 3
ESTAB      0      0               192.168.24.68:50606           42.54.109.216:80
ESTAB      0      0               192.168.24.68:51233           42.54.109.216:80
ESTAB      0      0               192.168.24.68:41312           42.54.109.216:80

# Count of active TCP connections keeps on increasing
❯ ss -tan | grep 42.54.109.216 | wc -l
130

• If the implementation takes longer to program the Gateway, the leaks end up exhausting the maximum number of active connections to a single host
  • The limit of maximum active connections to a single destination may either come from the client machine, or from any NAT system which sits in front of the client machine where the tests are run.
• On reaching the limit, we fail to make new HTTP requests and end up failing the tests.

Solution:

Solution is pretty straightforward: we disable HTTP keep-alives.

• Even right now, although we use HTTP keep-alive, we are actually not making use of this feature since we always create a new TCP connection for each HTTP request. This means the change does not have any adverse effect as we just closes the old TCP connections which we are no longer using.
• Given that we are just working with tests here, we may not want to over-optimize by reusing TCP connections and just use the simplest approach to fix this right now.

Which issue(s) this PR fixes:

Fixes #2357

Does this PR introduce a user-facing change?:

NONE

[howardjohn]

DisableKeepAlives part lgtm

[robscott]

Thanks @gauravkghildiyal!

[arkodg]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: arkodg, gauravkghildiyal, robscott

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• conformance/OWNERS [arkodg,robscott]

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[robscott]

Thanks @gauravkghildiyal!

/lgtm