cts: add TestLog tags to XML report


- When configured properly, TF can store logs and report the URLs where
  they are stored back to the test runner. So capture those URLs and
  write them to the XML report for future processing.

- CtsXmlResultReporter implements ILogSaver, which has a testLogSaved callback
  that gives the URL of the test log file. The URL to the test log is included
  in the test result XML when the test fails and when the feature is enabled.

- Add a new tag <TestLog> to represent selected logs that testLogSaved
  tells us about. Put all logic regarding this tag into the TestLog
  class. TestLogType is an enum that defines what specific logs we are
  interested in and how to identify them by examining the data name
  passed by the testLogSaved callback.

- Finally, add a "include-test-log-tags" flag to control whether these
  tags are enabled in the XML. This has the possibility of doubling the
  size of reports, so we will only enable this feature in the lab

Change-Id: Iecfa26abeee3a4d4d36dc95e5d0bfb5cac411236
6 files changed