patman: Don't buffer test output with a single test

patman: Don't buffer test output with a single test

When a single test is run we don't need to buffer the test output. This
has the unfortunate side effect of suppressing test output, in particular
the binman output directory normally printed with the -X option. This is
a huge problem since it blocks debugging of tests.

We don't actually know how many tests will be run when we set up the
suite, so as a work-around, assume that test_name being specified
indicates that there is likely only one.

Signed-off-by: Simon Glass <sjg@chromium.org>