internal/kokoro: make API incompatibility error clearer.
When dealing with breaking API changes, the kokoro logs are not
clear.  This adds a change to help log viewers identify that the
failure is due to incompatibility checking rather than an environment
or test failure.
@@ -33,6 +33,7 @@ for dir in $MANUALS $STABLE_GAPICS; do
# TODO(deklerk): there's probably a nicer way to do this that doesn't require
# two invocations
if ! apidiff -incompatible /tmp/pkg.master $pkg | (! read); then
+ echo "Detected incompatible API changes between master@HEAD and current state:"
apidiff -incompatible /tmp/pkg.master $pkg
exit 1
fi
