Fix requestId field

[AntoineJac]

after the commit (https://github.com/prebid/Prebid.js/pull/3411/files), Rubicon is no more seeing event for Server side requests.
This is due to the requestId not correctly set up as it should be the associatedBidRequest bidid not the bid response bid id.

Type of change

• Bugfix
• Feature
• New bidder adapter
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Does this change affect user-facing APIs or examples documented on http://prebid.org?
• Other

Description of change

• test parameters for validating bids

{
  bidder: '<bidder name>',
  params: {
    // ...
  }
}

Be sure to test the integration with your adserver using the Hello World sample page.

• contact email of the adapter’s maintainer
• official adapter submission

For any changes that affect user-facing APIs or example code documented on http://prebid.org, please provide:

• A link to a PR on the docs repo at https://github.com/prebid/prebid.github.io/

Other information

[idettman]

code LGTM, but it looks like unit tests need to be updated for this change.

[idettman]

After reviewing unit tests, they need to be updated for this change

[harpere]

Looks good, but needs tests. (also, don't think we need to update the legacy endpoint, but don't think it hurts)

[idettman]

After discussing with Antoine I'm approving as he mentioned

actually it is a little confusing as some code are using bid_id and sometime bidid…
I have added it some spec but haven’t changed the value as not sure it is the standard

[harpere]

LGTM