Johtaylo/issue1410

[johnataylor]

fixes #1410

This adds the UserAgent for the scenario where the client (specifically the BotFrameworkAdapter) has passed in a custom HttpClient.

Care needs to be take because the headers collection is not thread safe. The Adapter will be a singleton which is why this code is called from the constructor.

Ideally in the (dot net core) future we will be able to use IHttpClientFactory consistently.

[coveralls]

Pull Request Test Coverage Report for Build 53651

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 145 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 76.13%

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Files with Coverage Reduction	New Missed Lines	%
/libraries/Microsoft.Bot.Builder/BotFrameworkAdapter.cs	145	22.68%

Totals
Change from base Build 53546:	0.004%
Covered Lines:	4363
Relevant Lines:	5731

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💛 - Coveralls

[cleemullins]

No issues found in Microsoft.Bot.Builder.dll
No issues found in Microsoft.Bot.Builder.AI.Luis.dll
No issues found in Microsoft.Bot.Builder.AI.QnA.dll
No issues found in Microsoft.Bot.Builder.ApplicationInsights.dll
No issues found in Microsoft.Bot.Builder.Azure.dll
No issues found in Microsoft.Bot.Builder.Dialogs.dll
No issues found in Microsoft.Bot.Builder.TemplateManager.dll
No issues found in Microsoft.Bot.Configuration.dll
No issues found in Microsoft.Bot.Connector.dll
No issues found in Microsoft.Bot.Schema.dll

[EricDahlvang]

Seems legit to me. (When an HttpClient is passed in, we aren't adding the UserAgent headers ServiceClient adds by default, but it probably doesn't matter: https://github.com/Azure/azure-sdk-for-net/blob/master/src/SdkCommon/ClientRuntime/ClientRuntime/ServiceClient.cs#L575 )

Thanks for fixing this John!