Fix a bug with Canary becoming main server

[wayt]

What this PR does / why we need it:

A canary Ingress should never become a catch-all server if no other Ingress is a catch-all.

This PR prevent canary Ingress from becoming a catch-all server, or a server with a domain name if no regular Ingress is present.

Which issue this PR fixes

Special notes for your reviewer:

Cc @ElvinEfendi @clandry94

[wayt]

/assign @ElvinEfendi

[ElvinEfendi]

What do you think of filtering out canary ingresses right at the beginning of the function at https://github.com/kubernetes/ingress-nginx/pull/3521/files#diff-86ac9ff9d75a0c5005c116e766a6127dR885? That way we would not have to care about continueing in different loops inside the function.

[wayt]

@ElvinEfendi that would work too, but I find it less obvious for developers and debugging.
The current implementation gives us a log about why it doesn't use an Ingress to generate a server.

[ElvinEfendi]

/lgtm
/approve

[ElvinEfendi]

/hold

will wait for @clandry94 to 👍 first

for me LGTM

[ElvinEfendi]

/hold

will wait for @clandry94 to 👍 first

for me LGTM

[ElvinEfendi]

/hold

will wait for @clandry94 to 👍 first

for me LGTM

[ElvinEfendi]

/hold

[clandry94]

Looks good 👍 these new unit tests give me a lot more confidence too

[ElvinEfendi]

/hold cancel

[ElvinEfendi]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ElvinEfendi, wayt

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