Telaria Bid Adapter: add adCode & srcPageUrl query string param only once.

[vseventer]

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

This PR fixes a bug where the Telaria bid adapter includes the adCode and srcPageUrl query string parameters twice if added to the bidder params.

For example, the configuration below makes a request to (note &srcPageUrl=... is included twice):
https://test-supply-code.ads.tremorhub.com/ad/tag?adCode=test-ad-code&playerWidth=640&playerHeight=360&srcPageUrl=http://www.example.com&supplyCode=test-supply-code&adCode=test-ad-code&srcPageUrl=http://www.example.com&transactionId=5c5234a0-efc9-41a2-810d-defb5323c76e&referrer=http%3A%2F%2Fwww.example.com%2Freferer%2F&hb=1&fmt=json

{
  bidder: 'telaria',
  params: {
    supplyCode: 'test-supply-code',
    adCode: 'test-ad-code',
    srcPageUrl: 'http://www.example.com'
}

This PR fixes this issue, and only embeds srcPageUrl once:
https://test-supply-code.ads.tremorhub.com/ad/tag?adCode=test-ad-code&playerWidth=640&playerHeight=360&srcPageUrl=http://www.example.com&supplyCode=test-supply-code&transactionId=5c5234a0-efc9-41a2-810d-defb5323c76e&referrer=http%3A%2F%2Fwww.example.com%2Freferer%2F&hb=1&fmt=json

Note that, if params.srcPageUrl is not defined, the current default behavior applies (i.e. adding a srcPageUrl query string parameter containing document.location.href). params.adCode is a required field.

Other information

I had to update the Telaria tests to return a new stub object every time in order to make the tests idempotent.

[jsnellbaker]

LGTM