Fix router bug where cookie is not set correctly when dynamic changes are enabled

[ramr]

fixes bugz #1610712 - lil' bit of caveat here mentioned in the bugz.

/cc @openshift/sig-network-edge

[ironcladlou]

@pravisankar PTAL

[pravisankar]

Changes looks good but for the caveat, do you think that will be an issue when client caches cookie derived from blueprint route(pre-reload)?
Is this feasible?

• disable dynamic-cookie backend <blueprint-route>
• set dynamic-cookie-key backend <route-backend> ...
• enable dynamic-cookie backend <route-backend>

[ramr]

@pravisankar so the problem is the cookie name is tied to the backend and we can't change it dynamically(and there's the value part issue too).
When the route is added, a candidate route from the pool of available matching blueprint routes is picked up - let's say the cookie name N1 is basically the one associated with that backend _hapcm_blueprint_<name>_route_<nn>.
Example in bugz: d4bee9152b34dbe72ebd486a984a2809

Now when the router reloads, a new actual backend is added for the route with a different
cookie name say N2.
Example in bugz: 7ffbbf18807d0b625cf2fe2e2fe0ccf4

N1 != N2
And similarly for the value of that cookie -- which is really the hash for the backend server/pod which the session will stick to - that would change as well.

As re: the changes suggested - disabling the dynamic cookies on the blueprint route disable dynamic-cookie backend <blueprint-route> will make the session go to any of the backend server pods (remember the route is associated with a service and a service can have n pods backing it).
So that disables session stickiness while we are using a blueprint pooled route (for whatever the commit interval is set to - default 1 hour). And only enables it past the reload.

So my 2c here were:

1. Whilst we are using a blueprint route - let the session be sticky with one server pod.
2. And once the commit/reload happens, the session will still be sticky (but it could be to another server).
   The good part on 2 is that the stickiness name and value stays forever across any future
   reloads. Could change if a pod dies/ip changes etc but that's as normal.

[pravisankar]

/lgtm

Thanks Ram for the detailed explanation!

[ironcladlou]

/lgtm

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[pravisankar]

/retest

[ironcladlou]

/retest

[ramr]

/retest

[ironcladlou]

/retest