Add jshint diff-quality.

The platform includes jshint as a development tool, and our
builds are enforcing a limit on total number of jshint violations.
This commit will enforce no new jshint violations on a per-change
basis, much like pylint and pep8 are enforced. So with this change,
we'll be enforcing our linting requirements consistently, regardless
of type of violations.

Also on Jenkins, runs quality task after installing jshint.

scripts/generic-ci-tests.sh

@@ -67,8 +67,6 @@ case "$TEST_SUITE" in
         paver run_pep8 > pep8.log || { cat pep8.log; EXIT=1; }
         echo "Finding pylint violations and storing in report..."
         paver run_pylint -l $PYLINT_THRESHOLD || { cat pylint.log; EXIT=1; }
-        # Run quality task. Pass in the 'fail-under' percentage to diff-quality
-        paver run_quality -p 100 || EXIT=1
 
         mkdir -p reports
         echo "Finding jshint violations and storing report..."
@@ -76,6 +74,9 @@ case "$TEST_SUITE" in
         paver run_jshint -l $JSHINT_THRESHOLD > jshint.log || { cat jshint.log; EXIT=1; }
         echo "Running code complexity report (python)."
         paver run_complexity > reports/code_complexity.log || echo "Unable to calculate code complexity. Ignoring error."
+        # Run quality task. Pass in the 'fail-under' percentage to diff-quality
+        paver run_quality -p 100 || EXIT=1
+
         # Need to create an empty test result so the post-build
         # action doesn't fail the build.
         cat > reports/quality.xml <<END