test: Add a way to check part of a console line or skip it

Some lines of the output are not worth testing, or not worth testing in
their entirety. For example, when checking a hex dump we know that the
hex-dump routine can display ASCII so we only need to check the hex bytes,
not the ASCII dump. Add a new test macros which can check only part of
a console line.

Sometimes it is useful to skip a line altogether, so add a macro for that
also.

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