[PATCH v2 06/28] buildman: Add a test helper for creating a line prefix

[sjg at google.com]

The split/join code is repeated in a lot of places. Add a function to
handle this.

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

Changes in v2: None

 tools/buildman/test.py | 51 +++++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 20 deletions(-)

Applied to u-boot-dm, thanks!