patman: test_util: Use unittest text runner to print test results

The python tools' test utilities handle printing test results, but the
output is quite bare compared to an ordinary unittest run. Delegate
printing the results to a unittest text runner, which gives us niceties
like clear separation between each test's result and how long it took to
run the test suite.

Unfortunately it does not print info for skipped tests by default, but
this can be handled later by a custom test result subclass. It also does
not print the tool name; manually print a heading that includes the
toolname so that the outputs of each tool's tests are distinguishable in
the CI output.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>