Add option to show stdout, stderr

[aaaaalbert]

The current protocol for UTF is that when a unit test case prints to its stdout or stderr, the test case is considered to have failed (unless it specified the #pragma out or #pragma err directives, respectively.) The output and error streams are only shown for failed unit tests.

It might help for debugging purposes on new platforms or software versions to still print the output/error streams while test cases run. This should be done conditionally, e.g. when a -v/--verbose flag is provided to utf.py. Printing messages while running from within utf.py nicely combines the usual debugging approach with the framework's setup/subprocess/shutdown capabilities.

@rf1591, do you want to try your hand at this?