Re: dtc: More detailed testing of tree checks

So, like, the other day David Gibson mumbled:

This patch modifies the dtc-checkfails.sh testcase wrapper so that
instead of testing just that dtc fails with a particular error code on
the sample input, it scans dtc's stderr output looking for a message
that dtc failed a specific check or checks.  This has several advantages:
	- It means we more precisely check dtc's checking behaviour
	- It means we can check for generation of warnings using the
same script
	- It means we can test cases where dtc should generate
multiple errors or warnings from different checks

Signed-off-by: David Gibson <redacted>

Applied.

jdl