kokoro: Behave better on large diffs.
kokoro: Behave better on large diffs.

If the diff is very large, don't do a couple of things;
 * Output the patch into the console log.
 * Generate a pretty HTML version of the diff.

Signed-off-by: Tim 'mithro' Ansell <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mith.ro>

SymbiFlow/prjxray,SymbiFlow/prjxray,SymbiFlow/prjxray,SymbiFlow/prjxray,SymbiFlow/prjxray