test: Add helper to skip to partial console line

test: Add helper to skip to partial console line

Sometimes we need to skip to a line but it includes addresses or other
information which can vary depending on the runtime conditions.

Add a new ut_assert_skip_to_linen() which is similar to the existing
ut_assert_skip_to_line() function but only checks that the console line
matches up to the length of the provided string.

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