oeqa.buildperf: limit the length of error output

Limit the length of error logs to 40 lines. We don't need to
show/archive thousands of lines of bitbake logs if an error occurs.

(From OE-Core rev: 3f1996cb016713295edf35edc32dd5e84888a5c7)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/buildperf/base.py

@@ -36,7 +36,7 @@ log = logging.getLogger('build-perf')
 
 # Our own version of runCmd which does not raise AssertErrors which would cause
 # errors to interpreted as failures
-runCmd2 = partial(runCmd, assert_error=False)
+runCmd2 = partial(runCmd, assert_error=False, limit_exc_output=40)
 
 
 class KernelDropCaches(object):