Various fixes/improvements

[Avery-Dunn]

This PR handles a number of small issues from our backlog:

• https://github.com/AzureAD/microsoft-authentication-library-for-java/issues/726 : Removes an unnecessaries telemetry header
• https://github.com/AzureAD/microsoft-authentication-library-for-java/issues/741 : When a future was cancelled it shut down the relevant thread, however Java 9+ introduced timeout behavior that our code didn't consider so threads would continue through a timeout. We now check for exceptions (such as TimeoutException) as well as cancellations
• https://github.com/AzureAD/microsoft-authentication-library-for-java/issues/751 : Lowers the log level for successful cache lookup from 'info' to 'debug' to keep per-request logs more useful
• https://github.com/AzureAD/microsoft-authentication-library-for-java/issues/662 : Reduce verbosity of logs produced right before an exception, and avoid logging at an 'error' level if an exception will be thrown anyway